Directions:
1. Make the Dough:
In a small bowl, combine the lukewarm milk with the sugar and yeast. Stir gently and let it sit for about 5-10 minutes, until the mixture becomes frothy (this activates the yeast).
In a large bowl, whisk together the flour, salt, and lemon zest (if using).
Add the eggs, softened butter, vanilla extract, and the activated yeast mixture into the dry ingredients. Mix with a spoon or use a stand mixer fitted with a dough hook until the dough begins to come together.
Knead the dough on a lightly floured surface for about 10 minutes until it is smooth and elastic. If using a stand mixer, knead for about 5-7 minutes on medium speed.
Form the dough into a ball and place it in a lightly oiled bowl. Cover with a damp towel or plastic wrap and let it rise in a warm place for about 1-1.5 hours, or until it doubles in size.
2. Make the Pastry Cream (Crema):
In a medium saucepan, heat the milk and half of the sugar over medium heat. If using a vanilla bean, split it and scrape the seeds into the milk. If using vanilla extract, you will add it later.
In a separate bowl, whisk the egg yolks with the remaining sugar and cornstarch until smooth and pale in color.
Once the milk is warm but not boiling, slowly pour it into the egg mixture, whisking constantly to prevent the eggs from curdling.
Return the entire mixture to the saucepan and cook over medium heat, whisking constantly, until it thickens and begins to bubble. Continue cooking for 1-2 more minutes to ensure the cornstarch is cooked through.
Remove from the heat and stir in the butter until it melts and the mixture becomes smooth.
If you used a vanilla bean, discard the pod, and if you’re using vanilla extract, stir it in now.
Pour the pastry cream into a clean bowl, cover with plastic wrap (directly on the surface of the cream to prevent a skin from forming), and refrigerate for at least 2 hours until completely chilled.
3. Shape the Bomboloni:
Once the dough has risen, punch it down to release the air. Turn the dough onto a floured surface and roll it out to about 1/2-inch thickness.
Using a round cookie cutter or glass (about 2 to 3 inches in diameter), cut out rounds of dough. You should get around 12-14 doughnuts.
Place the dough rounds on a baking sheet lined with parchment paper, leaving some space between them. Cover the dough rounds with a clean kitchen towel and let them rise for another 30-45 minutes, or until puffy.