In a mixing bowl, combine the warm milk and active dry yeast. Let it sit for about 5 minutes until frothy.
In a separate bowl, whisk together the flour, sugar, and salt.
Add the eggs and melted butter to the yeast mixture and stir until combined. Gradually incorporate the flour mixture into the wet ingredients, mixing until a dough forms.
Knead the dough on a lightly floured surface for about 8-10 minutes until smooth and elastic.
Place the dough in a greased bowl, cover with a clean kitchen towel, and let it rise in a warm place until doubled in size, about 1-1.5 hours.
While the dough is rising, prepare the cream filling: In a chilled mixing bowl, beat the heavy cream and vanilla extract on medium-high speed until soft peaks form. Set aside in the refrigerator.
Once the dough has risen, punch it down and roll it out to about 1/2 inch thickness. Cut circles using a round cutter (about 3 inches in diameter).
Place the dough circles on a parchment-lined baking sheet, cover with a towel, and let them rise again for about 30 minutes.
In a deep pot, heat vegetable oil to 350°F (175°C). Carefully fry the doughnuts in batches until golden brown, about 2-3 minutes on each side. Remove and drain on paper towels.
Let the bomboloni cool slightly, then use a piping bag or a skewer to fill each doughnut with the whipped cream.
Dust the filled bomboloni with powdered sugar before serving.
Notes
Arrange bomboloni on a decorative platter and serve with additional powdered sugar and a side of fresh fruit for color.