In a large bowl, whisk together 1 cup flour, ¼ cup sugar, salt, and yeast. Add warm milk, 3 Tbsp melted butter, egg yolks, and vanilla. Stir until well combined and bubbly.

Stir in remaining flour until the dough forms and no longer sticks to the bowl. Knead for about 5 minutes gently in the bowl. Cover and let rise until doubled—about 45 minutes to 1½ hours depending on room warmth.

Preheat oven to 350 °F. Dust a work surface with flour, turn out the dough, and roll to about ½‑inch thickness. Cut into rounds (≈2.5″). Place on parchment-lined baking sheets. Cover and let rise ~30 minutes.

Bake for about 10–15 minutes until lightly golden. Immediately brush with melted butter, then roll generously in sugar.

Once cooled slightly, cut a small slit in each donut and pipe in jelly using a piping bag or tip until each is nicely filled.