Preheat the oven to 180℃ (170℃ fan)/350°F/gas mark 4.
Place the butter and sugar in a mixing bowl and beat until soft and well combined. Add the egg yolk and almond extract and most of the egg white. Beat to combine.
Add the flour and ground almonds and mix to form a smooth dough.
Divide into two pieces and roll out one half to fit a 20 x 30 cm (8 x 12in) cake tin.
Spread the mincemeat over the pastry. Then roll out the remaining pastry and lightly press on top.
Brush the top of the pastry with a little egg white, then sprinkle the almonds on top.
Mark into 16 bars. Bake for about 25 minutes or until golden. Allow to cool slightly in the tin before removing to a wire rack to cool.