Generously grease a bundt cake pan with a least 2 litre (8 cup) capacity with vegetable oil or non-stick baking spray. Lightly flour the bundt cake pan and shake out the excess flour.
Place all of the ingredients into the bowl of a food processor and blitz until the mixture is well-combined. The batter should be thick and smooth.
Alternatively, if you do not have a food processor:
Cream the butter and sugar in the bowl of a stand mixer with the flat paddle attachment.
Slowly beat in the flour, cocoa, sugar, baking powder, baking soda, salt and mixed spice.
Beat on low speed until all of the ingredients are incorporated.
In a small bowl or jug, lightly whisk together the sour cream, eggs and vanilla.
Slowly add the wet ingredients to the mixer, and beat until the batter is thoroughly mixed
To Bake the Chocolate Cake
Pour the batter into the prepared bundt cake pan, and give it a few taps on the kitchen counter to make sure the batter has settled into all of the grooves of the cake pan.
Bake for 45-55 minutes, or until a skewer inserted in the middle comes out clean.
Leave the cake to cool in the tin, on a wire rack, for about 10 minutes before carefully inverting the cake onto another wire rack to cool completely.
Dust with icing sugar (powdered sugar) before serving.
INGREDIENTS AT ROOM TEMPERATURE As for all cakes, make sure all of your ingredients, including the eggs and milk, are at room temperature before using.
OVEN TEMPERATURES All recipes on this website state temperatures for a regular oven (i.e. a conventional oven without fan). If you have a convection oven with a fan, please consult the manufacturer's handbook on how to adjust the temperature and baking time accordingly.