Set the oven to 190 C / Gas 5. Line a cupcake tin with 12 paper cases.
Beat the sugar and the butter together with the eggs, then add the remaining ingredients and blend well.
Divide the mixture between the paper cases, 1 tablespoon at a time.
Bake in the centre of the oven for 15 to 20 minutes - until slightly risen and golden brown. They need to be just about firm to the touch in the centre. Use the back of a small spoon to test, as the cupcakes will be hot.
Remove cakes from the oven and transfer them to a wire rack to cool.
Pipe a circular splodge of icing in the centre of the cupcakes (when cooled), and sprinkle the hundreds and thousands over the top.
Pop a marshmallow in the centre of the icing, and slightly push down to make it stick.