1. Add butter and confectioners’ sugar to a large bowl and mix until light and fluffy. Mix flour with baking powder and add together with the sour cream to the bowl and knead until you get a nice and smooth dough. Shape into a ball, flatten and wrap in plastic wrap. Place in the fridge for about 1 hour.

2. Preheat the oven to 350°F (180°C). Line a baking sheet with baking parchment and set aside. Roll out the dough on a lightly floured surface to a thickness of about 0.2 inches (0.5 cm) and cut out rings with a diameter of about 2 inches (5 cm). Mix the egg yolk and water in a small bowl, brush the dough rings with the egg wash and sprinkle with the pearl sugar. Place the rings on the baking sheet with some space in between and bake for 11-14 minutes until golden brown. Take out of the oven and let cool down a bit on the baking sheet, then transfer to a wire rack and let cool down completely. Repeat with the rest of the dough until all cookies are baked. Store in a tin box without other cookies.