1. Mix warm milk, melted butter, sourdough discard, sugar, and yeast in a large mixing bowl and let sit for a few minutes. Next, add flour and salt and mix with a dough whisk or wooden spoon until a slightly sticky dough forms and all ingredients are thoroughly combined.
2. Cover and let rise until doubled in size which should take 60-90 minutes.
3. At this point I like to pop it in the refrigerator overnight but you can proceed with the recipe if you want to skip that step.
4. After dough has doubled in size (or after chilling dough overnight), dump onto floured surface and press or roll out to about a 1-inch thickness. Cut rounds with a biscuit cutter or drinking glass/jar.* Reshape scraps by stacking them, re-rolling, and cutting. I like to get about 9-10 but if you like thinner English Muffins you can roll them a bit thinner and get a few more. This recipe is easily modified to your preferences.
5. When you have all muffins shaped, place them on a pan lined heavily with cornmeal or semolina flour. Dust both sides well. Cover the muffins and allow to rise for about an hour until puffy and light. If your dough came straight from the refrigerator this can take about 2 hours. You want these nice and puffy before you fry them.
6. Preheat an electric skillet to 300 degrees or a heavy skillet over medium-low heat, and place risen muffins in, leaving a bit of space between each one. Cover and cook for 5 minutes. Flip and cook on second side for another 5 minutes, covered. At this point I like to reduce the heat to about 250, flip the muffins a few more times until the internal temp registers 195-200 degrees F. You can also pop them in a 350 degree oven for about 10 minutes to finish cooking. This extra cooking time will depend on the thickness. I like mine on the thicker side so I almost always give them an extra few minutes. 
7. Remove to cooling rack and allow to cool to room temperature.
8. For the best craggy nooks and crannies, use a fork and your fingers to pry the halves apart before toasting.

*Alternative shaping option:

Rather than rolling and cutting into rounds, you can divide the dough into 8-12 pieces, form each piece into a ball, and press the ball into a flat disk. This is for the people who hate dealing with scraps.