Whisk the flour, sugar, yeast, and salt in the bowl of a stand mixer. Add the egg but DON'T stir in yet.
Heat the milk and coconut oil in a saucepan until a thermometer reads 110F. If the milk is too hot when you add it to the flour mixture, it will kill the yeast.
Pour the milk mixture into the flour mixture. Avoid pouring directly on the egg -- you don't want the hot milk to cook it.
Using the dough hook, mix on medium speed until the dough comes together and starts to pull away from the sides of the bowl, 3 to 4 minutes. Scrape down the sides with a rubber spatula, if needed. The dough will look a little irregular in texture.
Turn out the dough onto a lightly floured surface and knead until smooth, soft and elastic, 3 to 4 minutes. Shape into a ball and place in a large bowl lightly oiled with coconut oil; rub the top of the dough with a little more coconut oil. Cover with plastic wrap and let rise in a warm place until double in size, 1 to 2 hours.
Sprinkle 2 baking sheets with cornmeal and set aside. After the dough rises, punch it down and divide into 16 equal pieces. Roll each piece into a ball, then flatten into a 3-inch disk. Place the disks on the baking sheets.
Heat a 12-inch cast-iron skillet over medium heat. Coat the skillet with cooking spray and liberally sprinkle with cornmeal. Working in batches, cook the muffins until they are deep golden brown, 5 to 9 minutes per side. If they start to rise in a domed fashion, flatten with a spatula. To check for doneness, the internal temperature of a muffin - take a thermometer and go into the side of the muffin. The temperature should be at least 200F. If it is not, finish in a 350F oven for about 10 minutes. Let the English muffins cool completely, then split open with a fork, toast and serve with whatever topping you like.