Preheat oven to 170 C / Gas 3. Grease a 18cm (7 in) square cake tin and line with baking parchment.
Sift the flour, baking powder, cocoa into a bowl then add the margarine, sugar, eggs, vanilla extract and almonds (if using). Mix together with an electric mixer until all ingredients are well mixed and light and fluffy. Pour into prepared tin and level the surface.
Bake in the preheated oven for 20 to 25 minutes or until a skewer inserted into the centre comes out clean and firm to the touch. Remove from the oven and transfer to a wire rack to cool completely.
For the icing:
Place icing sugar and margarine into a bowl. Blend the drinking chocolate and hot water together and add with the milk. Beat together well until smooth. Spread the cooled cake with the icing and leave to set.
Sprinkle with icing sugar and cut into squares.
Alternatively use a shop bought chocolate fudge icing to spread on.
I used the Betty Crocker one it was gorgeous.