Preheat the oven to 375 F, Gas mark 5. Well grease a 7 inch sandwich tin. Prepare the pastry and line the tin. In a bowl, cream the butter with a wooden spoon, stir in sugar and beat in egg yolk and milk. Mix together the cocoa powder and the ground almonds, stir them into the mixture along with the vanilla essence. Blend well. Put the mixture into the pastry lined tin and cook for 20 minutes. Make the meringue mixture by whisking the egg white until stiff and then using a metal spoon, fold in the sugar. Remove the tart from the oven and cover the top with the meringue mixture, cook for a further 10 minutes. Allow to cool slightly before turning out. Serve the Chocolate and Almond Tart with double cream.