Step 1: In the bowl of a stand mixer or a large mixing bowl, combine the warm milk, melted butter, brown sugar, and active dry yeast. Stir gently and let sit for 5 minutes until the yeast becomes foamy.
Step 2: Add the sourdough discard to the yeast mixture and stir to combine.
Step 3: In a separate bowl, whisk together the bread flour and kosher salt. Gradually add the dry ingredients to the wet ingredients, mixing on low speed with a dough hook (or by hand) until a shaggy dough forms.
Step 4: Increase speed to medium-low and knead for 5-7 minutes (or knead by hand on a lightly floured surface for 8-10 minutes) until the dough is smooth, elastic, and pulls away from the sides of the bowl. It will be a slightly sticky dough.
Step 5: Lightly grease a clean bowl with oil, place the dough in the bowl, turning to coat. Cover tightly with plastic wrap or a damp towel and let rise in a warm place for 1.5 to 2 hours, or until doubled in size.
Step 6: Gently punch down the risen dough to release the air. Turn the dough out onto a lightly floured surface dusted with cornmeal. Roll the dough to about ½-inch thickness.
Step 7: Using a 3-inch round cutter, cut out English muffins. Gather the scraps, gently re-roll, and cut out more muffins until all dough is used. You should get 10-12 muffins.
Step 8: Transfer the cut muffins to a baking sheet lined with parchment paper and heavily dusted with cornmeal. Sprinkle the tops of the muffins with a little more cornmeal. Cover loosely with plastic wrap or a damp cloth and let rise again for 30-45 minutes, or until noticeably puffy.
Step 9: Preheat a heavy-bottomed skillet or electric griddle over medium-low heat. Cook the English muffins, without crowding the pan, for 5-7 minutes per side, or until golden brown and cooked through. If they brown too quickly, reduce the heat.
Step 10: Once cooked, transfer the English muffins to a wire rack to cool completely. Slice open with a fork to reveal those beautiful nooks and crannies, and enjoy!
Step 11: Store cooled English muffins in an airtight container at room temperature for up to 3 days, or freeze for longer storage.