Prepare the Dough: In a mixing bowl, cream together 125g (1/2 cup) butter, 100g (1/2 cup) sugar, 8g (1 tablespoon) vanilla sugar, and a pinch of salt.

Add 40ml (3 tablespoons) oil and mix until smooth.

Incorporate 1 egg white and blend well until combined.

Add 30g (1/4 cup) cornstarch, 4g (1 teaspoon) baking powder, and gradually mix in 320g (2 1/2 cups) of flour to form a soft dough.

Divide the Dough: Divide the dough into two equal portions for easier handling.

Shape the Cookies: Roll out the dough on a floured surface.

Cut out cookie shapes or roll the dough into balls, flatten slightly, and make a small indent in the center for the jam.

Add the Jam: Spoon a small amount of strawberry jam into the center of each cookie.

Bake: Place the cookies on a lined baking sheet and bake in a preheated oven at 170°C (338°F) for approximately 35 minutes, or until golden.

Final Touch: After removing from the oven, sprinkle the cookies with soft sugar while still warm.

Serve: Allow the cookies to cool slightly before serving.