Make the shortcrust pastry by putting the fats, flour and baking powder in a food processor and processing until it resembles fine breadcrumbs.
2 tablespoon cold water
Add cold water and pulse to bring the mixture together. Add a little more cold water if the pastry mixture still seems dry.
Remove from the food processor. Knead only very lightly, then wrap in plastic wrap and chill in the refrigerator for at least 20 minutes.
Remove from the fridge and divide the dough in two pieces. Roll out the dough and cut out two 20cm squares.
For the filling
Preheat the oven to 140C/160C fan (300F)
300 grams raisins, 150 grams currants, 30 grams mixed peel, 50 grams almonds, 75 grams plain (all purpose) flour, 60 grams light brown sugar, ½ teaspoon allspice, ¼ teaspoon ginger, 1¼ teaspoon black pepper, ¼ teaspoon bicarbonate of soda, ½ teaspoon cream of tartar
Weigh all the dry ingredients and place in a large bowl and mix the ingredients together to evenly combine.
1½ teaspoon brandy, 1 medium egg, 30 millilitres milk
Add the brandy, most of the beaten egg (keep a little back for glazing), and enough milk to moisten the mixture. Stir well to combine the wet and dry ingredients. The mixture should be moist but not very wet and sloppy.
Line the baking tin with baking parchment. l make a strip of baking parchment long enough that it sticks out both ends. This means that you can lift the black bun out of the tin easily.
Put one of the squares of pastry in the base of the tin.
Put the dried fruit mixture on top of the pastry and press down with the back of a spoon or a spatula.
1 medium egg
Prick the second piece of pastry all over with a fork, then put it on top of the dried fruit mixture. Brush with the remaining beaten egg.
Bake for 45 minutes. Check after 30 minutes and if the pastry is browning too much then cover the top loosely with foil.
Check if the bake is ready by inserting a skewer which should come out clean. If the cake is baked. If the skewer is wet and sticky then return the black bun to the oven and check again after 10 minutes.
Remove from the oven and leave to cool for 30 minutes in the tin. Then remove and cool on a wire rack.
When completely cool cut into 16 squares.
Notes
You can use ready-made shortcrust pastry. I recommend you use a plain unsweetened (not all butter) shortcrust pastry for this bake.