Mashed Potato Donuts with Vanilla Glaze

1. Place the potatoes in a large saucepan and cover with about 1 inch of water. Bring to a boil, reduce the heat, cover, and cook for 15–20 minutes or until fork-tender.
2. Drain, reserving 1/2 cup of the potato cooking water. Let the reserved water cool to 110–115°F, then mash the potatoes until smooth.
3. In a large bowl, dissolve the yeast in the reserved warm potato water. Add the mashed potatoes, warm milk, 1/2 cup canola oil, sugar, eggs, and salt.
4. Gradually mix in the flour until a soft dough forms. You may not need the entire 7 1/2 cups. Transfer the dough to a lightly greased bowl, turning once to coat.
5. Cover and let rise in a warm place until doubled, about 1 hour. Punch the dough down and let it rise again until doubled, about 20 minutes.
6. On a generously floured surface, gently spread or roll the dough to about 1 1/2–2 inches thick. Cut into donuts using a floured 3 1/2-inch donut cutter.
7. Heat frying oil to 350°F. Fry a few donuts at a time until deep golden brown, about 4 minutes per batch, turning halfway through. Keep the oil at or below 350°F so the centers cook through.
8. Whisk the confectioners’ sugar, water, and vanilla together until smooth. Dip the warm donuts into the glaze, then transfer to a wire rack and let the excess drip off.