Place the yeast, sugar, warm milk and warm water in the bowl of a stand mixer. Stir lightly with a fork and allow to sit for 10 minutes. It will begin to look foamy. If it doesn't, your yeast is likely dead and you should restart.
Add the apple cider vinegar, egg, and melted butter to the mixture. Use the paddle attachment and stir on low to combine wet ingredients. Slowly add the flour ½ cup at a time, and throw in the salt when half the flour is added. Mix on low until all the flour is incorporated, then increase to medium speed. Beat for 3-4 minutes until there are no dry spots and the dough is sticky, elastic, and smooth. Scrape down the sides of the bowl with a rubber spatula as needed. The dough will be quite loose, as seen in the process photos within the blog post.
Transfer the dough to a large oiled bowl and cover with plastic wrap or a kitchen towel. Place in a warm spot without drafts like the oven (turned off). Allow to double in size, which should take 1 hour.
Line two baking sheets with parchment paper and sprinkle with cornmeal. Transfer the risen dough to a liberally floured counter then gently pat down with floured hands until it’s about an inch thick.
Flour a 3 inch round cookie cutter and gently cut out the english muffins, one at a time. Carefully transfer each one to the prepared baking sheets using a spatula or bench scraper to help. The dough is very sticky. If the english muffins lose their shape, simply pat them into a circular shape on the baking sheet. Ensure you re-flour the cookie cutter and your hands before cutting each muffin. Press the scraps together and keep cutting until the dough is used up. You should get 10-12 english muffins. Cover the baking sheets loosely with a kitchen towel and allow to rise in a warm spot for 30 minutes.
Place a large cast iron skillet or griddle over medium-low heat. Once you can feel the heat from the pan, sprinkle the surface with cornmeal. Carefully place 3-4 english muffins on the pan, or as many that fit without crowding. Cook for 5-6 minutes, then flip and cook for another 5-6 minutes. You want the top and bottom to develop a deep colour. You'll find that the first batch will likely be the lightest as the pan heats up. Remove the cooked english muffins to a wire rack.
Discard the old cornmeal from the pan. Add a fresh handful to the skillet and cook the remaining english muffins. To prepare, split an english muffin in half with a fork for all the nooks and crannies, and enjoy warm or toasted with your choice of toppings! See notes below.