Italian croissants filled with silky pastry cream are the nation's favorite breakfast. These buttery mediterranean pastries are a family morning tradition.
Warm the milk just until lukewarm (about 100°F) and stir in active dry yeast and 1 tbsp of the sugar; let stand 5 minutes until frothy.
In a large bowl, combine flour, remaining sugar, salt, and lemon zest. Cut in the cold butter using your fingertips until the mixture resembles coarse crumbs.
Add eggs and vanilla to yeast mixture, whisk, then pour into the dry mix. Stir until dough forms, then knead for 8 minutes on a lightly floured surface until smooth and elastic.
Place dough in a greased bowl, cover, and proof at room temperature until doubled (about 90 minutes).
Punch down dough and roll into a 14-inch circle. Cut into 8 wedges. Place a heaping tablespoon of pastry cream on the wide end of each wedge, roll up toward the tip, and shape into crescents.
Transfer crescents to a parchment-lined baking sheet, cover loosely, and proof until puffy (about 45 minutes). Meanwhile, preheat oven to 375°F.
Brush each cornetto with beaten egg and bake in the center rack for 18–20 minutes, rotating halfway, until deeply golden.
Cool for 10 minutes, dust generously with powdered sugar, and serve slightly warm for best texture.