In the bowl of a stand mixer fitted with the dough hook, combine the warm milk, sourdough discard, yeast, and sugar. If using active dry yeast, let the mixture stand for 5–10 minutes until foamy. (Instant yeast can be mixed in immediately.)

Add the bread flour and mix on low speed until a shaggy dough forms.

With the mixer running on low, add the softened butter in 2–3 additions, allowing each addition to fully incorporate before adding more. Add the salt while incorporating the butter. Don't worry if the dough loosens and looks a little messy after adding the butter—that's completely normal. Keep the mixer running, and within a few minutes, the dough will come back together into a smooth, elastic ball.

Increase the mixer to medium-low speed and knead for 6–8 minutes. The dough should feel soft but a little firmer than cinnamon roll or dinner roll dough. It should clean the sides of the bowl and lightly slap against the mixer while still feeling slightly tacky to the touch. Resist the urge to add extra flour unless the dough is very sticky.

Transfer the dough to a lightly greased bowl, cover, and let it rise until doubled in size, about 60–90 minutes.

Turn the dough onto an unfloured work surface. I like to weigh the entire dough before dividing it into 12 equal pieces. During testing, each English muffin typically weighed between 74–76 grams, but every batch is a little different, so simply divide your total dough weight by 12.

Shape each piece into a smooth, tight ball.

Place the cornmeal in a shallow plate or shallow pasta bowl. Place one dough ball onto the cornmeal and gently press it down until it's about 3–3½ inches across. Flip it over and coat the other side before transferring it to a parchment-lined baking sheet. This method coats and shapes the English muffins at the same time, so there's no need to roll out the dough or use a biscuit cutter. Repeat with the remaining dough.

Cover loosely with a lid, lightly greased plastic wrap, or a clean kitchen towel. Let the English muffins rise until they're noticeably puffy and no longer feel cool to the touch, about 45–75 minutes depending on your kitchen.

Preheat the oven to 350°F and place a wire rack inside a rimmed baking sheet.

Heat a large cast iron skillet or heavy-bottomed skillet over medium to medium-low heat. Lightly coat the skillet with a small amount of butter and a drizzle of neutral oil.

Cook 3–4 English muffins at a time until the bottoms are lightly golden, about 3–5 minutes. If your skillet develops hot spots, rotate the muffins halfway through cooking for more even browning. Flip and cook the second side until lightly golden, but don't worry about developing a deep crust since they'll finish baking in the oven.

As soon as one batch comes off the skillet, transfer the muffins directly to the prepared wire rack and place them in the oven while you continue cooking the next batch. Baking each batch immediately keeps the muffins at a similar starting temperature and helps them finish more evenly. Bake for 5–8 minutes, or until the centers reach 200–205°F.

Repeat with the remaining batches, adding a little more butter and oil to the skillet as needed.

Transfer the English muffins to a cooling rack and allow them to cool completely. For the best nooks and crannies, split them with a fork rather than slicing them with a knife.