In the bowl of your stand mixer, add the flour, warm milk, egg, butter, sugar, yeast, salt, and baking powder. Using the paddle attachment on medium-low, mix the ingredients until just combined. Switch to the dough hook attachment and mix on medium-low (#2 setting) for 7 minutes, until the dough is elastic and not sticky to the touch.
2½ cups all-purpose flour, ¾ cup whole milk, 1 large egg, 1 tbsp unsalted butter, 1 tbsp sugar, 2 tsp instant yeast, 1 tsp Kosher salt, 1 tsp baking powder
Remove the dough from the bowl and use your hands to form it into a ball.
Liberally grease a large bowl with cooking spray and rotate the dough ball in the bowl to cover it with cooking spray. Lightly spray the top of the dough with a little more cooking spray. Cover tightly with plastic wrap and place in the refrigerator overnight, or in a warm, non-drafty area for 1 to 2 hours, until the dough has nearly doubled in size.
Cooking spray
If the dough has been proofed (rested) in the refrigerator overnight, take it out and let it sit on the counter for at least an hour to become room temperature.
In a small bowl, mix together the semolina and cornmeal until combined.
⅓ cup semolina flour, ⅓ cup cornmeal
Sprinkle a light layer of the semolina/cornmeal mixture over your griddle.
Use a paper towel to lightly grease the insides of the rings with softened butter.
softened butter
Turn the dough out onto a lightly floured surface. Pinch off 2.5 ounces of the dough (about the size of a golf ball) and use the palm of your hand or a rolling pin to flatten the ball into a thin circle (about ¼-inch thick). Place the circle of dough in one of the buttered rings and place it on the prepared griddle. Repeat with the remaining dough (you should have enough dough for 8 muffins). Cover loosely with plastic wrap and place the griddle in a warm, non-drafty area for 20 minutes.
Preheat oven to 350°F. (If proofing the muffins in the oven, don't turn the oven on until you remove them.)
Remove the plastic wrap from the muffins and turn the griddle to medium-low (about 275), or place the cast-iron griddle over medium-low heat on the stove. Use your hands to gently move the rings around on the griddle, for even browning. Cook for 7 minutes, and carefully flip them over (the bottoms should be nicely browned). Carefully remove the rings and cook for another 5 to 7 minutes, until both sides are golden brown.
Sprinkle more of the semolina/cornmeal mixture over a baking sheet. Place the muffins on the sheet and cover tightly with aluminum foil. Bake for 7 to 10 minutes, until the inside of the muffins reach 190°F.
Remove the muffins from the oven and let them cool on a baking sheet.
Use your hands or a fork to split the muffins. If desired, toast until lightly browned. Serve at once.