Preheat oven to 180°C (160°C fan) mark 4. Put all the biscuit ingredients into a food processor and pulse until the mixture clumps together. Tip the dough on to a work surface and bring together.
Step 2
Roll out the dough on a sheet of baking parchment, trying to keep it rectangular and dusting your rolling pin with flour as needed, then trim to a 23cm x 30.5cm (9in x 12in) rectangle. Cut the rectangle lengthways into 3 even strips, keeping strips together, then cut across them at 2.5cm (1in) intervals, keeping the rectangles together. If you like, use the end of a skewer to mark the long edges of each biscuit with five dots to resemble a traditional Bourbon. Chill for 30min.
Step 3
Bake for 25min, then carefully remove the tray from the oven and cut through the marks to make sure biscuits are separated. Leave to cool completely.
Step 4
To make the filling, put the butter into a large bowl and sift in the icing sugar and cocoa powder. Mix until combined (don't be tempted to add any liquid - the icing should be thick).
Step 5
Sandwich the cooled biscuits together with the chocolate filling, using a piping bag if you want a neater finish.
An experienced and highly skilled team of food writers, stylists and digital content producers, the Good Housekeeping Cookery Team is a close-knit squad of food obsessives. Cookery Editor Emma Franklin is our resident chilli obsessive and barbecue expert, who spends an inordinate amount of time on holidays poking round the local supermarkets seeking out new and exciting foods. Senior Cookery Writer Alice Shields is a former pastry chef and baking fanatic who loves making bread and would have peanut butter with everything if she could. Her favourite carb is pasta, and our vibrant green spaghetti is her weeknight go-to. Lover of all things savoury, Senior Cookery Writer Grace Evans can be found eating crispy corn and nocellara olives at every opportunity, and will take the cheeseboard over dessert any time (though she cannot resist a slice of tres leches cake). With a wealth of professional kitchen know-how, culinary training and years of experience between them, they are all dedicated to ensuring every Good Housekeeping recipe is the best it can be, so you can trust they’ll work (and if they don’t – we’ll have the answer for why*) every time (*90% of the time the answer is: “buy an separate oven thermometer”!).
