Measure 1 cup plus 2 tablespoons whole milk into a microwave-safe bowl or measuring cup. Heat in 30-second increments on high until the milk is warm but not hot (test with a fingertip—should feel warm, not uncomfortable).
Stir 1/4 cup sugar into the warm milk until dissolved. Sprinkle 2 1/4 teaspoons active dry yeast over the milk, stir gently once or twice, then let the mixture sit undisturbed for 10 minutes (it should become foamy).
In a small bowl, whisk 2 large eggs with the 10 tablespoons melted unsalted butter (melted and slightly cooled). In a separate bowl, whisk together 4 cups all-purpose flour and 1/2 teaspoon fine sea salt. Set both bowls aside.
Fit an electric mixer with the dough hook. Add the egg/butter mixture to the mixer bowl. Turn the mixer to medium-low and, with the mixer running, pour in the yeast/milk mixture. Let the hook mix this for about 1–2 minutes to combine.
With the mixer still on medium-low, add the flour mixture in 1/4- to 1/2-cup increments, allowing each addition to incorporate before adding more, until all the flour is added.
Stop the mixer and scrape down the bowl and dough hook. Turn the mixer on medium-low and knead for 5 full minutes.
Stop the mixer, scrape the bottom and sides of the bowl, then run the mixer on medium-low for an additional 30 seconds.
Turn off the mixer and let the dough rest, undisturbed in the mixer bowl, for 10 minutes.
Lightly oil a clean bowl. Transfer the dough to the oiled bowl, turning it gently to coat all sides with oil. Cover the bowl tightly with plastic wrap.
Place the bowl in a warm, draft-free spot and let the dough rise until doubled in size, about 1 hour. (If your kitchen is cold or drafty, place the covered bowl in the oven with only the oven light on; do not turn the oven on.)
After the dough has doubled, gently deflate it (press down once or twice to release large air bubbles). Cover and refrigerate the dough for at least 8 hours or overnight.
The next day, turn the chilled dough out onto a lightly floured work surface. Roll the dough to a thickness of 1/4 to 1/3 inch.
Using a 3-inch cutter, cut as many doughnut rounds as possible. Re-roll scraps as needed and continue cutting. Use a 1-inch cutter to cut the center hole from each round and to cut doughnut holes from the scraps.
Place the cut doughnuts and doughnut holes on a lightly floured baking sheet, spaced so they are not touching. Cover the sheet with a clean tea towel and let rise in a warm place until visibly puffed and airy, about 1 to 1 hour 15 minutes.
When the doughnuts are nearly finished rising, heat canola oil in a large, heavy-bottomed pot to 375°F (190–191°C). Use enough oil to give the doughnuts room to float freely (at least 1 quart is a good guideline). Keep a thermometer in the oil and do not allow it to exceed 380°F.
Fry 1–2 doughnuts at a time (do not overcrowd). Gently lower each doughnut into the hot oil and cook about 1 minute per side, turning once, until golden brown. Doughnut holes will cook faster—about 30 seconds per side.
Use a slotted spoon to remove fried doughnuts and holes, letting excess oil drip back into the pot. Transfer them to several layers of paper towels for initial draining. Wait about 5 seconds, flip each once more onto a clean part of the paper towels for another 5 seconds, then move the doughnut to a wire rack set over a rimmed baking sheet to catch drips. Repeat with remaining pieces.
Let the doughnuts cool slightly while you make the glaze.
Whisk together 3 cups sifted powdered sugar, 1/8 teaspoon fine sea salt, 1/2 teaspoon pure vanilla extract, and 1/2 cup milk until completely smooth.
One at a time, dip each doughnut into the glaze so it is submerged about halfway; completely submerge the doughnut holes and remove with a slotted spoon. Allow excess glaze to drip back into the bowl, then place glazed doughnuts right-side up on the wire rack. The rimmed baking sheet will catch drips.
Let the glaze set briefly, then serve the doughnuts warm if possible, or at room temperature.