Combine the cake flour, fine sugar, and baking powder in a food processor. Make sure to blend the dry ingredients well to ensure they are evenly distributed.
Then, put the food processor on its pulse setting. While it's running, add in the cold cubed butter. Continue using until you have a crumbly sand-like texture.
Next, combine the egg yolks and sour cream together in a separate bowl. Slowly add the egg mixture to the food processor while it is running at a low speed. Add liquid until the mixture is just combined.
Wrap the sweet pastry dough in plastic wrap and rest it in the fridge for 1 hour.
Once the pastry has rested, preheat the oven to 350°F (180°C). Brush a springform cake pan with softened butter. Make sure to brush the sides as well.
Then, evenly roll out the sweet pastry on a lightly floured surface. Roll it until it is big enough to line the entire bottom and sides of the cake pan.
Next, lay the pastry sheet inside the pan. Make sure it is pressed against all the edges. You can crimp the sides if you'd like.
Dock the bottom of the crust with a fork. Then, partially bake the crust for 10 minutes. Once par-baked, remove it from the oven and allow it to cool.
First, blend the cottage cheese in the food processor until you have a smooth lump-free consistency. Set the cheese aside until needed.
Then, in a large mixing bowl, beat the egg whites until they reach stiff peaks. Set aside the whipped egg whites until needed.
Then, in another large bowl, cream the butter and sugar together until they become light and fluffy. Add the vanilla extract and egg yolks and mix well.
Next, fold in the blended cottage cheese mixture until it is fully incorporated. Finally, gently fold in the whipped egg whites.
Once your par-baked sweet pastry has completely cooled, you can add the cheesecake batter into the pan.
This Sernik recipe bakes for roughly 50-60 minutes. The top shouldn't be allowed to brown.
After 45 minutes, you will need to add the sour cream topping.
While the cheesecake is baking, make the sour cream topping. Simply whisk together all of the topping ingredients and set it aside until needed.
After the cheesecake has baked for 45 minutes, add the sour cream topping over it and continue baking it for the remaining time.
After the cheesecake has been fully baked, turn off the oven and allow it to completely cool. After 1 hour, remove it and continue cooling the Polish cheesecake at room temperature for another hour.
Then, while the cheesecake is still inside of its pan, wrap it with plastic or saran wrap. Allow the cheesecake to set in the fridge for 6 hours, but preferably overnight.