Night 1: Build Levain (10:00 PM) Whisk 10 g sourdough starter into 50 g water, then stir in 50 g bread flour. Cover loosely and let ferment at room temperature 74–78°F (23–26°C) for 8–10 hours until peak volume (at least triples).

Day 2: Mixing & Fermentation Boil & Mash (7:00 AM): Boil potatoes until tender, drain thoroughly, and mash until completely smooth. Let cool to room temperature. Autolyse (8:00 AM): In stand mixer bowl, combine 100 g active levain, 100 g milk, 2 eggs, 500 g all-purpose flour, 50 g sugar, 2 g optional yeast, and 250 g cooled mashed potatoes. Mix into a shaggy mass, cover, and rest for 30 minutes. Mix & Salt (8:30 AM): Knead on low speed (or KitchenAid speed 3) for 3–4 minutes. Add 10 g salt and mix for 2 more minutes until a ball forms. Butter Integration: Add 75 g softened butter and knead on medium-high speed for 10–15 minutes until smooth and glossy. (If dough remains overly sticky after 10 minutes, add 20–40 g extra flour). Bulk Proof (9:00 AM): Cover and proof at 76–80°F (24–28°C) for 3–4 hours, performing 2 stretch-and-folds during the first 2 hours until slightly puffy. Cold Retard (12:00 PM): Transfer covered dough to refrigerator for 8–10 hours.

Shaping & Overnight Pan Proof Shaping (10:00 PM): Roll cold dough onto a floured surface to ½–1 inch thickness. Stamp out donuts using a donut cutter or glass. Transfer shaped donuts onto individual parchment squares. Pan Proof: Cover loosely and let proof overnight on the counter at 72–73°F (22–23°C) until expanded and puffy.

Day 3: Precision Frying & Glazing Preheat vegetable oil in a deep fryer or heavy pot for 30 minutes until hot. Fry donuts for 1–2 minutes per side until golden brown. Drain on a wire cooling rack. Whisk 170 g powdered sugar, 30 g melted butter, and 1½ tsp vanilla extract until smooth. Dip warm donuts into the glaze and serve!