In the bowl of a stand mixer fitted with the paddle attachment, beat bread flour, warm milk, egg, butter, sugar, yeast, salt, and baking powder at low speed until combined. Switch to the dough hook attachment. With mixer on medium-low speed, beat until smooth and elastic, about 5 minutes. Spray a large bowl with cooking spray. Place dough in bowl, turning to grease top. Cover and let rise in refrigerator overnight. (Alternatively, cover and let rise in a warm, draft-free place [75°F/24°C] until doubled in size, about 1 hour.)

In a small bowl, whisk together semolina flour and cornmeal. Sprinkle a layer of semolina mixture over a well-seasoned cast-iron griddle. Line a rimmed baking sheet with parchment paper. Sprinkle semolina mixture over prepared baking sheet. Butter 8 (3¾x1-inch) English muffin rings. For a small, single-burner griddle, place 4 rings on griddle; set aside remaining 4 rings. For a large, double-burner griddle, place all 8 rings on griddle.

Let dough come to room temperature. On a lightly floured surface, divide dough into 8 equal portions. Shape each portion into a ball, and roll each ball into a 3½-inch disk. Place 1 disk in each prepared muffin ring. Sprinkle tops lightly with semolina mixture. Cover loosely with plastic wrap, and let rise in a warm, draft-free place (75°F/24°C) for 20 minutes.

Preheat oven to 350°F (180°C).

Place griddle on stove, and heat over medium-low heat, allowing muffins to come to temperature with pan. Cook, moving pan around occasionally for even heat, until muffins are golden brown on bottom, 5 to 7 minutes. Turn muffins, and remove rings; cook until golden brown on both sides and an instant-read thermometer inserted in center registers 190°F (88°C), about 5 minutes more. If muffins register below 190°F (88°C) but are golden brown, place on prepared baking sheet, and cover with foil.

Bake for 5 to 10 minutes. Let cool completely on a wire rack. If using a single-burner griddle, remove pan from heat, and allow to return to room temperature. Wipe pan clean, and sprinkle with remaining semolina mixture. Place remaining 4 muffins on griddle.

Place griddle on stove, and heat over medium-low heat, allowing muffins to come to temperature with pan. Repeat procedure as directed. Store in an airtight container for up to 5 days.