Rum and Raisin Chocolate Biscuit Bars

The second Signature Challenge of Bake Off 2019 was to make 12 decorated chocolate biscuit bars. We saw many delicious looking creations on the show, my personal favourites were Michelle’s Bakewell Bars, Rosie’s Virgin Mojito Bars and Helena’s Witchy Fingers (mainly because they had matcha!!). I took inspiration from my favourite ice cream flavour, rum and raisin, and transformed it into these utterly delicious Rum & Raisin Chocolate Biscuit Bars!

Two layers of buttery and rich raisin brown sugar shortbread sandwiched together with marshmallow and salted rum caramel all covered with dark chocolate and finished with a further drizzle of the salted rum caramel and some rum caramel popcorn. This is really luxurious and a special treat, a bit fancier and more technical than most of my recipes on my blog but well worth the time to make it!

During my experimentation, my first batch of these went pretty dreadful because I added caramel directly to the marshmallow too early which was too warm and the whole thing went to liquid so this recipe development process took me about 6 hours in total. But once I learnt from my mistakes, then it was a pretty easy time! I also had a problem with the crumbliness of the shortbread so made sure I worked it a little bit more to build up the structure, as well as make sure that the raisins didn’t keep breaking the biscuit’s surface!

Last year’s Biscuit Week Technical was Wagon Wheels (and you can check out my homemade version without gelatine) and I realised that my chocolate biscuit bar has turned into a fancier version of the wagon wheels, not that that is a bad thing! For this recipe, the marshmallow has gelatine in it for a better set which holds nicely and prevents any spilling out the side. The recipe makes more marshmallow than is required so simply pour the remaining mixture into a baking tin lined with parchment dusted well with icing sugar and cornflour, dust the top with more icing sugar and cornflour and leave to set before slicing into squares, tossing lightly in more icing sugar and cornflour.

The only other strange step in my recipe is putting the demerara sugar into the food processor before using it. I do this to make the granules of sugar slightly smaller so it can dissolve more easily into the margarine/butter in the biscuit and you don’t end up with specks of sugar in the final biscuit. Using demerara sugar also gives that hint of caramel flavour in the biscuit that compliments the rum and raisin flavour.

Now unlike most of the bakers in the show, I cover the assembled biscuit bars in melted chocolate rather than place the biscuits and filling into a silicone mould lined with chocolate and turn out the bars. My method is suited to people without silicone moulds. If you do want to try these bars with a mould and using a chocolate shell, then you can follow the same recipe but you will need to prepare the chocolate shells first. You can read a little bit more about this in my Dark Chocolate Teacakes recipe.

Tempering the chocolate is probably the favoured procedure here such that the finished biscuit bars are coated in chocolate that have a snap and a nice shine. I microwave the chocolate and heat it just to the point where most of the chocolate has melted and use the residual heat of the bowl and chocolate to melt the remaining chocolate. Covering the bars in chocolate can be tricky if the chocolate isn’t too liquid so I cover and finish the bars one at a time. If you don’t have the time to make this all in one go, then the caramel and shortbread can be made ahead of time; the rum caramel should be stored covered in the fridge and the shortbread kept in an airtight container.

Check out my video guide on making my Rum and Raisin Chocolate Biscuit Bars below!

For the rum caramel

200g granulated sugar
1 tbsp honey
30g margarine/unsalted butter
120ml double cream
¼ tsp table salt
½ tsp vanilla extract
2 tbsp dark rum

For the raisin shortbread

60g demerara sugar
120g margarine
200g plain flour
40g raisins

For the marshmallow filling

12g powdered gelatine
85ml cold water
1 tbsp dark rum
200g granulated sugar
1 tbsp honey
100ml cold water
1 large egg white
½ tsp vanilla extract

For the decoration

200g dark chocolate
Sweet popcorn

First prepare the rum caramel, so that it has enough time to cool down for use. In a large non-stick frying pan, add the sugar in an even layer over the base of the pan and the honey. Place over a medium heat and cook until the sugar and honey have melted together and it is a deep golden caramel, without stirring the sugar, only swirling the pan.

Remove from the heat and add the margarine and whisk until it is incorporated. Pour in the double cream (ideally as cold as possible) and return to a medium heat, cooking the mixture while stirring until the caramel is a nice golden amber colour and thicker. Turn off the heat and add in the salt, vanilla extract and the rum and whisk to combine. Pour out into a large bowl and leave to cool at room temperature. When the caramel has cooled down, cover with clingfilm.

Preheat the oven to 180˚C. Line a baking tray with baking parchment.

In a food processor, blitz the demerara sugar for about 30 seconds until its texture is slightly finer; you’re not looking for icing sugar, just slightly smaller granules. Add this to the margarine and mix the two together until slightly lighter in colour. Add in the plain flour and raisins and combine until it begins to form clumps and no flour is visible. Tip the whole mixture out onto a lightly floured surface and bring the dough together into a smooth ball.

On a lightly floured surface, roll out the dough to 6mm thick, turning regularly to avoid sticking to the surface. Using a cutout measuring 8cm by 5cm, trim as many biscuits from the dough as possible and place onto a baking tray lined with parchment, leaving some room between for spreading. Reroll the offcuts until you have 12 biscuits.

Bake the raisin shortbread for around 15 minutes until the shortbread is lightly golden at the edges and feels set. Leave to cool on the baking tray for about 5 minutes before carefully transferring to a cooling rack to cool fully. Once they are cool, match two biscuit halves together that are similarly sized and choose a top and bottom half (it doesn’t matter too much which is which as it’s all being covered in chocolate anyway!).

When the biscuits and caramel are nice and cool, prepare the marshmallow filling. In a small bowl, mix the gelatine powder with the 85ml water and rum to bloom the gelatine. Set aside but have on hand. In a large clean mixing bowl, whisk the egg white until it looks frothy.

Place the sugar, the honey and the water into a medium saucepan over a medium heat and bring to the boil, swirling the pan occasionally. Using an instant read thermometer, keep an eye on the temperature of the sugar syrup. When it reaches 120˚C, turn off the heat and stir in the gelatine until dissolved.

Turn on the electric whisk and gradually pour the sugar syrup into the egg white while whisking continuously, avoiding the whisk itself. Continue to whisk for about 8 – 10 minutes until the marshmallow is thick and glossy. It may look like nothing is happening but the mixture will begin to hold the shape of the whisk as it cools and sets. Add in the vanilla extract and whisk again. Leave the marshmallow to cool for about 5 minutes before placing some into a piping bag. Cut off a 1cm hole from the end and leave for about 10 minutes (see above to see how to use the remaining marshmallow mixture).

Pipe some marshmallow onto each of the bottom biscuits, leaving about half a centimetre from the edge. Place some of the salted rum caramel into a piping bag and drizzle some generously over the marshmallow. Press the top biscuits down onto the bottom halves, pushing down slightly so the marshmallow reaches the edge of the biscuit. Place into the fridge for 30 minutes to chill.

Melt the chocolate until it has a pouring and coating consistency (you can temper this but you don’t have to). Place the biscuit bars on a cooling rack which has a sheet of baking parchment underneath to catch any excess chocolate that drips off. Working with each biscuit bar individually, cover the entire bar in the melted chocolate, making sure that the whole bar is covered (to the best of your ability), pushing off any excess and letting it drip off. Drizzle more of the caramel diagonally over one corner and place pieces of popcorn on the other half, drizzling more caramel over – see photos for reference!

Transfer the bars carefully to a plate or a small metal tray and refrigerate for an hour or until the chocolate has set. Serve the biscuit bars as a fancy dessert with some ice cream perhaps or as a fancy treat on their own with a cup of tea!

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Cake Week: Black Sesame and Matcha Angel Cake Slices
Bread Week: Tangzhong Chinese Tear and Share Buns
Dairy Week: Millionaire’s Coconut Ice Shortbread or Spiced Fig and Yoghurt Cake with Yoghurt Buttercream
1920s Week: Piña Colada Custard Tarts
Dessert Week: Pistachio Matcha Layered Meringue Cake
Festival Week: Sweet Potato and Taro Tangzhong Buns
Pastry Week: Butternut Squash Pie
Patisserie Week: Domed Princesstårta Tartlets
Finals Week: Triple Layer Chocolate Drip Cake

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