Preheat oven to 350F/180C.

Grease bottom and sides of an an 8-inch/20cm springform pan and line the bottom and the sides with parchment. When you line the sides, you are making a collar that will be for later use when you top the cake with the mousse.

Place the cocoa in a large bowl. Stir in the boiling water and mix until a paste forms. Add the sugar, flour, butter and eggs. Beat until smooth.

Spread the batter in the prepared pan, leveling the top surface as best you can.

Bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean.

Brush the orange liqueur or brandy if using, over the top of the hot cake. Cool cake completely.

To make the mousse, place the chocolate morsels in a bowl and melt over a pan of gently simmering water, stirring until it's melted and smooth. Microwave melting is NOT recommended because this needs gentle even heat so the chocolate does not become grainy. Let the chocolate cool slightly.

Whip the heavy cream until soft peaks form. Fold in the melted chocolate into the cream, making sure it's blended well and not streaky.

Spoon mousse on top of cooled cake and level the top. Chill for at least 4 hours, preferably overnight.

Remove cake from pan and discard parchment. Place on a serving dish and dust with a bit of sifted cocoa. Top with raspberries and dust with confectioners/icing sugar.