In a bowl of a stand mixer, add in the warm milk, yeast, sugar, salt and mix well. Let it rest for about 10 minutes until it foams.
Add in the eggs, flour and mix well until a soft dough forms.
Add in the butter and knead for about 6-8 minutes.
Transfer the dough to an oiled boil and cover and let rest for about 1.5- 2 hours.
Punch the dough and divide into 12 equal pieces (85 grams each).
Pinch the edges of the small dough ball into the middle, forming a small pouch. Place the ball, seam side down on a clean work surface, your hand over it and lightly roll into a ball.
Place each ball on parchment paper and cover and let it rest for 30-40 minutes.
Heat the frying oil to 180 degrees Celsius. Place a maximum of 2 donuts at a time, to give it space to rise and puff up. Fry for about 3-4 minutes on each side.
Remove from the oil and let it drain the excess oil on paper towels or a wire rack.
While still warm, toss them in white sugar and make sure they are well covered.
Allow them to cool completely before filling them with jam.
Insert the pastry tip into the side of each donut and firmly squeeze a few tablespoons of jam into the center.
Serve while warm!