Viennese Shortbread

Cream together soft butter, sugar, salt, and vanilla sugar until light and fluffy.

Add eggs and beat until smooth and well combined. Mix in the baking soda with vinegar (or if using baking powder, sift it into the flour instead).

Sift the flour and bring the dough together. You don't need to knead it much—it'll be soft and come together into a nice ball.

Wrap in plastic and chill for 30 minutes. Once chilled, roll out the dough to about 5mm thick (adjust the thickness based on your baking sheet size). Bake at 350°F for about 15 minutes.

While the cake is still warm, carefully split it in half. Spread two-thirds of the jam on one half, then gently place the other half on top and spread the remaining jam on the surface.