Pour the milk into a small saucepan, add the butter, and heat gently until the butter melts. Then leave it to cool down to just warmer than room temperature.
In a bowl of a stand mixer, mix the flour, sugar, salt and yeast.
Pour in the milk mixture, add the egg yolks and, fitted with a dough hook attachment, run the mixer for 10-12 minutes, until the dough starts gathering around the hook, looks shiny, and feels soft and elastic. It's not a stiff dough, but don't be tempted to add more flour.
Scoop the dough into a clean bowl, cover with a damp tea towel or plastic wrap and leave it in a warm spot to rise for 1-1.5 hours until it doubles in volume.
In the meantime, mix the farmer's cheese, sugar, sour cream and egg yolks in a large bowl. Use a fork or a potato masher to combine everything (the mixture may still look a little grainy depending on the type of farmer's cheese you used).
Once proofed, divide the dough into 5 equal pieces and shape them into balls.
Place the balls on a large baking sheet lined with parchment paper, making sure to leave plenty of space in between.
Using a large spoon, press the middle of the ball dough to create a bowl.
Spread 1 teaspoon of jam in the groove, then spoon the farmer's cheese filling on top.
Leave the filled buns in a warm spot to proof again for 30 minutes.
In the meantime, preheat the oven to 180°C (350°F).
Brush the sides of the buns with a little milk, and place them in the oven for 20 minutes.
Leave the buns to cool down for 10 minutes on the baking sheet, then transfer onto a wire rack to cool down completely.