In a large mixing bowl, combine the all-purpose flour, sugar, and yeast, creating a well in the center. Warm the milk and melt the butter together until just lukewarm, then pour into the well along with the eggs. Mix until a dough forms, then knead it on a floured surface for about 10 minutes until smooth and elastic. Place the dough back in the bowl, cover with a damp cloth, and let it rise in a warm area for 1-2 hours or until doubled in size.

After the dough has risen, gently punch it down to release the air and turn it out onto a floured surface. Roll the dough out to about 1-inch thickness and use a cookie cutter to cut out circles. Gather the scraps, re-roll them, and cut additional circles. Place the cut doughnuts on a parchment-lined baking sheet and cover them with a kitchen towel. Allow them to rise for another 30 minutes until puffy.

In a deep frying pan, heat oil to 350°F (175°C). Carefully add several doughnuts at a time, making sure not to overcrowd the pan. Fry the Bomboloni alla Crema for about 2-3 minutes on each side until golden brown, flipping with a slotted spoon. Once fried, transfer them to a plate lined with paper towels to drain excess oil and cool slightly.

Once the doughnuts have cooled enough to handle, fill a pastry bag fitted with a long tip or use a doughnut injector filled with custard cream. Poke a hole into the side of each Bomboloni and gently squeeze to fill until you feel slight resistance. Be careful not to overfill; you want a rich filling without it spilling out.

Finally, dust the filled Bomboloni alla Crema with powdered sugar just before serving. Use a sifter for an even coating, enhancing their presentation and adding a touch of sweetness. These delightful treats are best enjoyed warm, showcasing their fluffy texture and creamy interior.