Preheat the oven to 180 C / Gas 4. Line a 12-hole muffin tin with paper cases.
Cream the butter and sugar together in a large mixing bowl. Add the flour, bicarbonate of soda, mixed spice and eggs and mix well. Stir in the mincemeat. Using a tablespoon, spoon the mixture into the cases, filling to 2/3 full to allow for a good rise.
Put the tins in the oven on the middle shelf and bake for 20 to 25 minutes. Remove the buns from the oven and sprinkle with icing sugar. Leave to cool.