In a large bowl, combine 1 cup of flour, 1/4 cup of granulated sugar, 1 envelope of fast acting yeast and 1/4 teaspoon of salt
Warm up 2/3 of a cup of milk to about 100 degrees F (this should take about 30 seconds in the microwave)
Add the warmed milk to the dry ingredients along with 3 tablespoons of melted butter, 2 egg yolks and 1/2 of a teaspoon of vanilla extract and mix well to ensure everything is fully combined
Cover the bowl tightly with plastic wrap and allow it to sit at room temperature for about 10 minutes. You are looking for some bubbles to form over the surface
Add 1 1/2 cup of flour, mix to incorporate and begin kneading in the bowl with clean hands
If the dough is sticking to your hands, add a bit of flour (as little as possible) until the dough can be kneaded without sticking to your hands
Cover the bowl with plastic wrap, then top with a kitchen towel and allow the dough to rest at room temperature for about 90 minutes
Once the dough has doubled in size, transfer it to a lightly floured work surface and roll it out to a large circle about 1/2" in thickness
Cut round circles of dough with a large round cookie cutter. If you use a 2 1/2" or 3" cutter, you should get 12 doughnuts. You can gather and roll out the remaining dough and cut additional doughnuts, if possible
Place the doughnuts on to a parchment lined baking sheet and cover the baking sheet with a light kitchen towel and allow them to rest until they are puffed up (about 45 minutes)
Preheat your oven to 375 degrees while the doughnuts are resting
Once the doughnuts have puffed up, bake them on a middle rack at 375 degrees for between 10 and 12 minutes or until the doughnuts become lightly golden
Transfer the baked bomboloni onto a cooling rack