Warm the milk: Heat the milk until warm to the touch, about 105–110°F. It should feel cozy, not hot. This helps the yeast activate without killing it.

Make the dough: In a large bowl, whisk the flour (start with 3 1/2 cups), cornstarch, sugar, yeast, and salt. Add warm milk, melted butter, eggs, and vanilla. Stir until a shaggy dough forms.

Knead until smooth: Knead by hand 7–9 minutes or in a mixer with a dough hook for about 5–6 minutes. The dough should be soft, slightly tacky, and elastic. If very sticky, add flour 1 tablespoon at a time. Avoid over-flouring; a soft dough makes lighter donuts.

First rise: Place dough in a lightly greased bowl, cover, and let rise in a warm spot until doubled, 60–90 minutes. A slow, steady rise builds flavor and tenderness.

Roll and cut: Turn dough onto a lightly floured surface. Roll to about 1/2-inch thick. Cut 3-inch rounds, then cut 1-inch holes in the centers. Gather scraps and re-roll once for best texture.

Second rise: Place donuts and holes on parchment-lined sheets. Cover lightly and let rise until puffy, 30–45 minutes. They should look airy and slightly jiggly when you nudge the tray.

Heat the oil: In a heavy pot, heat 2 inches of oil to 350–360°F. Keep a thermometer clipped to the side. Stable oil temperature is the difference between greasy and perfect.

Fry the donuts: Fry 2–3 at a time, about 45–60 seconds per side, until light golden. The donuts should puff and float. Use a slotted spoon to transfer to a wire rack set over a sheet pan. Fry donut holes for 30–45 seconds total.

Make the glaze: Whisk powdered sugar, corn syrup, vanilla (1 teaspoon), and 6 tablespoons water or milk until smooth. Add liquid 1 teaspoon at a time until the glaze is pourable but not watery. Thin glaze = classic melt-in texture.

Glaze while warm: Dip each warm donut entirely in the glaze, flip to coat, and let excess drip off. Place back on the rack. For extra shine and that signature sweetness, double-dip after 2–3 minutes.

Let set and enjoy: Give the glaze 10–15 minutes to set. The donuts will still be soft and warm inside with a delicate, crackly finish outside.