Melt the butter and mix it together with the kefir and sugar in a large mixing bowl.
Combine the rest of the dry ingredients in a separate bowl and then add them to the butter mixture. Stir until the batter is fully smooth - you can also use your hands for this.
Wrap the dough in plastic wrap and store in the fridge overnight.
Preheat oven to 390°F (200°C) and line a baking sheet with baking paper.
Roll out the dough on a floured surface. Use the cookie cutters to cut shapes out of the cookies. Bake for 7-10 minutes, until the edges start to get crispy but not brown. The center will remain soft.
After the cookies have cooled, use the food coloring to paint decorations on them.