Grease and line a 12" x 9" traybake tin
Start by making the pastry. Rub the butter into the plain flour and caster sugar until it resembles breadcrumbs. You can use your fingers or a food processor to do this. Add the cold water (or milk) and bring the mixture together to form a dough
Tip the dough into the tin and spread it out into an even layer, pressing it down with your fingers until compact and even. Prick it all over with a fork. Chill it in the fridge for 30 minutes. Meanwhile, pre-heat your oven to 160C Fan/180C/350F/Gas Mark 4
Bake the pastry for 20 minutes, or until lightly golden on the edges, take it out and set aside. Leave your oven on
Make the sponge by mixing the butter and the golden caster sugar together, ideally using an electric mixer for 3 minutes
Mix in the eggs and almond extract
Gently whisk or fold in the ground almonds, baking powder and self raising flour
Spoon the mincemeat over the pastry base and spread it out
Gently spoon the cake batter over the top and spread it out into an even layer. Sprinkle over the toasted flaked almonds
Bake for 35 minutes or until it is a lovely golden brown all over, and a skewer inserted in the centre comes out clean. Leave to cool completely in the tin
When fully cool, mix the icing sugar with water and pipe it over the sponge in a zig zag pattern
Cut into squares and serve. Store leftovers in an airtight container for up to 3 days