Gingerbread Sheet Cake

First, preheat the oven to 180 °C and line a baking sheet (20 cm × 30 cm) with baking paper.

Sift plain flour, Dutch cocoa, sugar, and gingerbread leavening powder into a large bowl. Mix with a whisk.

Crack 1 egg into a taller container and mix it with 120 ml of rapeseed oil, 50 ml of milk, 200 ml of kefir, and 1 teaspoon of vanilla extract. Pour the wet ingredients into the bowl with the dry ingredients and mix.