Bake the doughnuts for 12-15 minutes until risen and dark golden. Let the doughnuts cool for a few minutes, then brush with the melted butter and roll in sugar. Spoon a little raspberry jam into the piping bag and the peanut butter in to another piping bag. Poke a hole in each doughnut, then push in the nozzle and squeeze in a little jam, but do not fill the doughnut completely. Repeat this process with peanut butter until the doughnut is completely filled. Best served warm.