Preheat the oven to 180C (fan oven 160), gas 4. Line 12 cupcake tins with paper cases.
In a large bowl, mix together the marmalade, golden syrup, sugar and oil. Put the ginger in a small measuring jug and pour over 125ml (4fl oz) boiling water. Stir in the bicarbonate of soda and pour onto the marmalade mixture, whisking all the time until smooth.
Whisk in the flour, cinnamon, pepper and cloves, followed by the egg.
Divide the mixture between the cupcake cases and bake in the oven for 12-15 minutes until risen and firm to touch. Cool on a wire rack.
To decorate, gradually beat the cream and 1 teaspoon of icing sugar into the mascarpone to make a smooth frosting.
Slice the rounded top off about half of the cupcakes and stamp out a hole in the centre using a small pastry cutter. Sandwich the top back on the base with a little of the cream frosting and spoon some marmalade into the hole. Dust the top lightly with icing sugar.
With the remaining cupcakes, put a scoop of frosting on the top of each one and smooth with a round-bladed knife. Roll the outer edge of the frosting in the toasted nuts.
Prepare ahead: The cupcakes can be made and kept in an airtight container, in a cool place, up one day ahead. Alternatively, freeze the undecorated cupcakes for up to 1 week.