Add sourdough discard, milk, sugar, all-purpose flour and butter to a large mixing bowl. (DO NOT add baking soda and salt at this point. Those ingredients are added after bulk rise.)
Mix ingredients together to form a sticky dough.
Cover bowl with plastic wrap and a tea towel and let rise at room temperature for 6-12 hours (or refrigerate overnight).
After bulk rise/or next day, sprinkle salt and baking soda onto dough and gently knead or mix until combined. (I find it easiest to use a large spoon.)
Line a cookie sheet with parchment paper and sprinkle cornmeal over the entire cookie sheet. Set aside.
Turn the dough out onto a floured surface.
Sprinkle the top of your dough with a little more flour. It tends to be sticky. Flour a rolling pin and roll out dough to 1/2 – 3/4-inch thick (depending how thick you like your muffins).
Dip biscuit cutter (or you can use a glass) into all-purpose flour and cut muffins. (You may not need to dip the cutter into flour if they’re not sticking.)
Place each muffin on the parchment-lined cookie sheet about an inch apart. Sprinkle the top of each muffin with more cornmeal to prevent sticking.
Cover muffins loosely with plastic wrap and let them rest for 30-45 minutes.
Spray a cast iron skillet or nonstick pan with nonstick cooking spray and heat on medium-low heat. (I use an electric skillet.)
Remove plastic wrap from muffins. (They should look a little puffy.)
Cook muffins for 5-7 minutes per side until golden and the centers are cooked through. If they are browning too fast, you may need to lower the heat.
After 5-7 minutes, when you see them starting to puff up, go ahead and check the underside and see if they are ready to flip.
Transfer English muffins to a cooling grid until cool enough to handle.
To get those signature nooks and crannies you often see with English muffins, use a fork to split the muffin all the way around and pull open. Serve with butter and jam.
Enjoy!