Using a beater, cream the butter and sugar. Add the egg and then the milk and dry ingredients, alternating between the two.
Put a little of the resulting batter in the bottom of each cup of a greased muffin pan. Add 1 tsp of jam on top of the batter in the middle. Put more batter on top.
Bake for 25 minutes or until cake tester or toothpick comes out clean.
When baked, brush the tops of the doughnuts with melted butter and then sprinkle on the sugar-cinnamon mixture.
Carefully slide a butterknife around the edge of the muffin cups and gently lift the doughnuts out.