Activate the Yeast: In a small bowl, combine the warm milk and yeast. Let it sit for 5–10 minutes until frothy.

Make the Dough: In a large mixing bowl or stand mixer, whisk together 3 ½ cups of flour and sugar. Add the yeast mixture, eggs, softened butter, vanilla extract, and salt. Mix until a sticky dough forms.
If using a stand mixer, switch to the dough hook and knead for 8–10 minutes, adding more flour (1 tbsp at a time) as needed until the dough is smooth and elastic.
Transfer the dough to a lightly oiled bowl, cover with a clean kitchen towel, and let it rise for 1–1.5 hours or until doubled in size.

Shape the Bomboloni: Punch down the risen dough and turn it onto a lightly floured surface. Divide the dough into 12–15 equal portions (about 2-inch balls). Roll each portion into a smooth ball.
Place the balls on a parchment-lined baking sheet, leaving space between them. Cover and let them rise for another 30–45 minutes until puffy.

Fry the Bomboloni: Heat about 2–3 inches of oil in a deep skillet or pot over medium heat to 350°F (175°C).
Carefully fry the dough balls in batches, turning occasionally for 2–3 minutes per side until golden brown. Avoid overcrowding the pan.
Use a slotted spoon to transfer the fried Bomboloni to a paper towel-lined plate to drain excess oil.

Fill and Coat: Once the Bomboloni have cooled slightly, use a sharp knife or piping bag tip to cut a small hole in the side of each.
Insert the piping bag filled with your chosen filling (custard, Nutella, jam, etc.) and pipe generously into the center.
Dust the filled Bomboloni with powdered sugar or drizzle with melted chocolate/glaze before serving.