Cut 200g butter into small pieces. In a bowl, combine the butter, 350g wheat flour, 150g powdered sugar, 1 packet vanilla sugar, and 1 egg. Knead until the dough comes together. Cover and refrigerate for 1 hour.
Preheat oven to 175°C (347°F). Roll out the dough on a 40 x 30 cm baking sheet lined with baking paper. Bake for 25 minutes.
Let the baked dough cool for 5 to 10 minutes. Cut it lengthwise into 4 equal rectangles.
Mix water and powdered sugar to make frosting.
Spread jam on 2 rectangles and frosting on the other 2. Stack each frosting-topped rectangle on top of a jam-topped rectangle. Cut each stacked pair into 5 sections for 10 pieces total.
Optionally sprinkle colored sugar pearls on the pieces.