Put flour with baking powder in a mixing bowl and mix. Add the remaining ingredients and use a hand mixer (dough hook) to form a dough, first on the lowest, then on the highest setting. Wrap the dough in cling film and put it in the fridge for 30 minutes.
Then roll out the dough on a lightly floured surface to about 3 mm thin and divide with a pastry wheel into 4.5 cm x 3.5 cm rectangles. Place half of the rectangles on a parchment-lined baking sheet. Put a hazelnut-sized dollop of jam on each with the help of 2 teaspoons. Now place the remaining rectangles on top and press down on the edges.
Bake in a preheated oven at 200 ° C top / bottom heat (hot air: 180 ° C, gas: level 3 - 4) for about 10 minutes.
Bake on the middle shelf and sprinkle with the decorative sugar immediately after baking. Then let cool on a cake rack.