In a large bowl, whisk together the flour, sugar, instant yeast, and salt until evenly combined.

In a separate bowl, whisk the warmed milk, eggs, and softened butter until smooth and slightly foamy.

Pour the wet mixture into the dry ingredients gradually. Stir to combine, then turn the dough onto a lightly floured surface and knead for 5–7 minutes until smooth and elastic.

Place the dough in a lightly oiled bowl, cover with plastic wrap or a clean towel, and let it rise in a warm spot until doubled in size — about 60–90 minutes.

Gently deflate the dough and roll it out to about 1/2-inch thickness. Cut into 2.5–3 inch circles using a cutter.

Place a teaspoon or so of filling in the center of half the circles. Top with the remaining circles and pinch the edges tightly to seal.

Place the filled rounds on a baking sheet, cover lightly, and let them rise for 20–30 minutes.

Heat oil in a deep fryer or heavy-sided pot to 350°F (175°C). Fry the paczki in batches, 1–2 minutes per side, until deep golden brown.

Remove with a slotted spoon and drain on paper towels. Dust generously with powdered sugar and serve warm.