Beat the butter and both sugars in a large bowl using an electric whisk until creamy. Add the egg yolks and vanilla, whisk to combine, then add the flour, custard powder, a grating of nutmeg, the cinnamon and a pinch of salt. Mix until everything clumps together into a dough.

Roll small pieces of dough into cherry-sized balls (about 10g each), then arrange on a baking tray lined with baking parchment. Squash each down slightly using a fork. Chill for at least 30 mins or up to a day. Will keep frozen for two months.

Heat the oven to 180C/160C fan/gas 4 and bake for 12-15 mins until golden and firm to the touch. Cool completely, then dust the tops lightly with icing sugar.

For the filling, beat the ingredients together using an electric whisk until smooth, then spoon into a piping bag fitted with a large round nozzle. Pipe a dot of icing on the flat side of half the cookies. Sandwich with the plain cookies. Will keep in an airtight container for three days.