To make the mincemeat, place the fruit and Walnuts in a large bowl with the brandy, orange zest and juice and leave to soak for 1 hour. Stir in the remaining ingredients and allow to soak overnight, stirring occasionally. You can use the mincemeat the following day, or store in sterilised jars for later. (See Cook’s tip).
For the lattice pastry, place the 50g Walnuts in a food processor and finely chop. Add the flour, a pinch of salt and the butter and pulse to form fine breadcrumbs, add in the egg yolk and 2-3 tbsp water and pulse until a soft dough is formed. Wrap in clingfilm and chill for 30 minutes.
Preheat the oven to 200oC, gas mark 6.
Roll out ¾ of the pastry and line a 23cm fluted tin, chill for 10 minutes. Prick the base with a fork and line with a large scrunched-up piece of baking parchment, add baking beans and bake for 10 minutes, remove the parchment and beans and cook for a further 5 minutes.
Fill the pastry case with mincemeat and top with the clementine slices. Roll out the remaining pastry including any off cuts from the base to a 23×15 rectangle and cut into 1cm strips. Arrange these strips in a lattice design over the mincemeat, top with a few whole Walnuts. Bake for 25 minutes until golden. Cool a little in the tin before removing to serve.
