Beat the softened butter with sugar until very creamy. Beat in the egg. Mix baking powder with flour and fold into the egg-butter mixture.
Now form ping-pong ball sized balls from the dough and press them flat on a baking tray covered with baking paper. Use your thumb to press a hollow in the center of the cookies.
Put about a teaspoon of jam into it. Bake in oven preheated to 160°C (convection oven) for approx. 15 min.