In a blender or mixing bowl, combine 2.5 cups of flour, a pinch of salt, 0.5 tsp of baking powder, and 125 g of cold diced butter.
Process the mixture until it resembles fine crumbs. You can also rub the butter into the flour by hand.
Add 2 eggs and 3/4 cup of kefir (or sour cream) to the crumbly mixture.
Knead the mixture into a soft and smooth dough. Wrap in plastic wrap or place in a bag and refrigerate for 30 minutes.
While the dough is chilling, prepare the filling. Melt 125 g of butter in a pan. Add 1 cup of flour, 1/2 cup of sugar, and 2 tsp of vanilla sugar (or natural vanilla). Mix until smooth and spreadable.
Divide the chilled dough into 2 or 3 parts. Roll each portion into a flat rectangle about 3–4 mm thick. Divide the filling accordingly and spread evenly over each dough sheet.
Optionally, sprinkle chopped walnuts over the filling before rolling.
Roll the dough sheets into logs. Brush each roll with egg yolk. Slice into 7–8 equal pieces.
Place the sliced rolls cut-side down on a baking sheet lined with parchment paper.
Bake in a preheated oven at 175°C (350°F) for 20–25 minutes, or until golden brown.
Allow the gata to cool completely. Store in an airtight container or plastic bag to prevent drying out. Gata will stay fresh for several days.
