Instruction

1. Whisk together milk, yeast, and 1 tablespoon sugar in bowl of a stand mixer until combined. Gradually stir in 2 cups flour using a rubber spatula until a dough forms, about 1 minute. Cover bowl; let rise in a warm place (about 75°F) until mixture is puffed with some small bubbles peeking through surface, about 30 minutes.
2. Place bowl on stand mixer fitted with the paddle attachment. Add eggs, melted butter, salt, vanilla, and remaining 1/4 cup sugar; beat on low speed just until combined, about 15 seconds. With mixer running on low speed, gradually add 3 1/3 cups flour, beating until dough comes together, about 30 seconds. Fit dough hook attachment on mixer; beat on medium-low speed until a soft, slightly sticky, elastic dough forms, 8 to 10 minutes, stopping to scrape down sides as needed. Pinch off a small piece of dough (about the size of a quarter) using lightly floured hands. Slowly pull dough out from center. If it can stretch thin and transparent like a window pane, the dough is ready. If the dough tears, beat 1 more minute, adding additional flour if needed, and check again. Add up to remaining 1/3 cup flour, 1 tablespoon at a time.
3. Grease a large bowl with oil and place dough in bowl. Cover and let rise in a warm place (about 75°F) until puffed, about 20 minutes. Gently punch down dough; cover and let rise in a warm place until puffed, about 20 minutes. Gently punch down dough. Cover and let rise in a warm place until doubled in size, 45 minutes to 1 hour.
4. Place a fine wire-mesh strainer over a medium bowl; line strainer with 4 layers of cheesecloth, leaving a 4-inch overhang on all sides. Place ricotta in strainer. Wrap cheesecloth around ricotta; top with a small bowl weighed down with heavy cans. Let drain 30 minutes.
5. Stir together drained ricotta, sugar, raisins, egg yolk, lemon zest, vanilla, and salt in a medium bowl until well combined.
6. Line two baking sheets with parchment paper. Turn dough out onto a lightly floured surface; divide into 14 pieces, keeping dough covered with plastic wrap or a clean kitchen towel while working. Shape pieces into smooth balls. Place balls on prepared baking sheets at least 1 1/2 to 2 inches apart; cover and let rise in a warm place until puffed, 40 to 45 minutes.
7. Preheat oven to 350°F with racks in upper third and lower third positions. Whisk together egg yolk and 1 teaspoon water in a small bowl.
8. Firmly press center of 1 dough ball using floured bottom of a small glass to create an indentation; use fingertips to expand the depression to a 2 1/2-inch-wide x 3/4-inch-deep well. Spread about 2 tablespoons cheese filling evenly in well. Brush dough with egg yolk mixture. Repeat process with remaining dough balls, cheese filling, and egg yolk mixture.
9. Bake in preheated oven until fluffy and golden brown, 20 to 24 minutes, rotating baking sheets between top and bottom racks halfway through baking time. Let cool on baking sheets on a wire rack 15 minutes. Serve warm or let cool to room temperature, about 30 minutes.