Sugar-dusted filled doughnuts popular in northern Italy are light, pillowy, and irresistible. These mediterranean pastries are a family Carnival and everyday treat.
Warm the milk to about 110°F (just warm to the touch) and stir in the yeast with 1 tablespoon of sugar; let it stand for 7–10 minutes until bubbly.
In a large mixing bowl, combine flour, salt, and lemon zest. Stir in the yeast mixture, eggs, softened butter, and the remaining sugar until a sticky dough forms.
Knead the dough on a lightly floured surface for 8–10 minutes until smooth and elastic. Place in a lightly oiled bowl, cover, and let rise in a warm spot until doubled, about 1–2 hours.
Punch down the risen dough, roll it to about 1/2 inch thick, and cut out rounds with a 3-inch cutter. Place on parchment, cover, and rise again for 30–45 minutes until puffy.
Heat the vegetable oil in a deep pot to 340–350°F. Fry the Krapfen in small batches for 2–3 minutes per side until golden brown, turning once for even coloring. Drain well on paper towels.
While still warm, fill each Krapfen with fruit preserves using a pastry bag with a long tip. Generously dust with powdered sugar before serving.