In a small bowl, mix together the flour and baking powder. Set aside.
In a separate mixing bowl, beat the butter, powdered sugar, and salt with an electric mixer until fluffy and smooth.
Add 1 egg and beat until mixed. Divide other egg, add the egg white and reserve the egg yolk for later use. Mix to combine.
Gradually mix in dry ingredients, then knead dough until it forms a firm but cohesive dough. Wrap in plastic wrap and chill while you work on the filling, about 30 minutes.
Preheat the oven to 350°F and line a baking sheet with parchment paper.
Use an immersion blender to roughly blend the cottage cheese to make a smoother consistency. You can also mash curds with a fork.
Mix in egg, sugar, sour cream, and flour. Mix until well combined. Set aside.
Roll the dough out to ¼ inch thickness. Using a circular or crinkle cutter, cut 4-inch circles of dough.
Place circles on prepared baking sheet. Spoon 2 tablespoons of filling mixture on half of each circle.
Fold empty dough half over the filling and press down lightly. Brush cookies with reserved egg yolk.
Bake until golden and puffed, 20-25 minutes. Enjoy!
