1. Preheat an oven to 180 degrees (fan). Grease and line a square 20cm x 20cm cake tin with baking parchment.

2. Either melt the chocolate in a microwave using short bursts of heat and stirring at intervals or place the chocolate pieces in a bain marie (a bowl set over a pan of lightly simmering water) to melt. Once melted, remove from the heat and set it aside for five minutes.

3. With an electric whisk, in a large mixing bowl, cream the butter and sugar together until it is pale and fluffy. Add the vanilla extract.

4. Stir the melted chocolate into the creamed mixture, then mix in the eggs gradually.

5. Sieve the flour, cocoa powder and salt together, then mix the sieved ingredients into the cake batter until fully combined. Loosen the batter with a little milk if required.

6. Spoon the chocolate batter into the lined tin and level the surface with the back of a wet spoon. Bake in the preheated oven for 20 minutes, until risen in the centre and a skewer inserted into the centre comes out clean. Set aside in the tin to cool fully.

7. Once cooled, remove the cake from the tin and peel away the paper lining.  Place on a chopping board. Use a serrated knife to slice through the centre of the cake to give two slim layers. Freeze both layers for 30 minutes to firm up.

8. To assemble: remove the ice cream from the freezer and allow it to sit out for five to 10 minutes to soften slightly. Clean the square cake tin and line it with a double layer of clingflim, leaving overhanging edges. Place the base layer of cake inside the tin. Spread the slightly softened ice cream over the cake base. Lay the top layer of cake over the ice-cream filling and wrap up tightly by folding in the overhanging clingfilm.

9. Freeze for five hours before serving.

10. To prepare sandwiches, cut parchment paper into individual squares, slice the cake into 10 individual slices, wrap neatly in paper and tie up with string.

Variation

Make a plain Madeira cake and use raspberry ripple ice-cream as the filling.