Preheat the oven to 170C/325F/gas mark 3. Thoroughly grease a 10 cup bundt tin.
Whisk together the butter and sugar with an electric mixer until pale and fluffy; Whisk in the eggs one at a time, beating well after each addition.
In a separate bowl, sift together the flour, baking powder, mixed spice and salt. Fold 1/3 of the flour mixture into the butter mixture, followed by 1/2 the buttermilk then another 1/3 of flour, then the remaining buttermilk and flour.
Mix through the mincemeat then pour the batter into the prepared tin and level the surface. Bake for 60-75 minutes until a skewer inserted into the center comes out clean and the cake is starting to pull away from the sides of the tin. Cover the top loosely with tin foil partway through baking if it starts to get too dark.
Remove the cake from the oven and leave to cool in the tin for 15 minutes then carefully turn out onto a wire rack to cool completely.
To make the glaze, place the sifted icing sugar in a bowl and gradually stir in the whisky or orange juice until it forms a runny icing. Drizzle over the cake and serve. Store in an airtight container.