In a medium mixing bowl, mix the sourdough starter, water, and yogurt. In a large mixing bowl, combine the dry ingredients: the all-purpose flour, whole wheat flour, sugar, salt, and baking powder.

Pour the wet ingredients into the dry ingredients, and mix with a stiff silicone/rubber spatula or wooden spoon until it forms a soft shaggy dough. You can also do this in a stand mixer with the dough hook attachment.

Knead with the rubber spatula, floured hands, or the dough hook attachment for 5 minutes. Cover the dough (a loose, clean plastic grocery bag works well), and let it ferment in a warm place (75-80°F/24-26°C) for 1 hour. We put the dough in a closed microwave next to a big mug of just-boiled water.

After 1 hour, stretch and fold the dough: lift the dough vertically, stretching and folding the dough over to the other side. Continue to repeat this lift, stretch, and fold motion 4-5 times, rotating the bowl each time.

Cover the dough with a clean plastic grocery bag, and let it ferment on the counter overnight (as long as the ambient temperature ranges from 65-70°F/18-21°C—any warmer, and you risk it overproofing) for 8-12 hours.

After 8-12 hours (i.e. the next morning), you MUST work with the dough quickly to prevent it from overproofing. The dough will be very puffy and full of air. Punch the air out, using a stiff silicone/rubber spatula to fold the dough over onto itself until you have a ball of dough.

Spread the semolina onto a large rimmed sheet pan. On a lightly floured surface, use a floured rolling pin to roll the dough out to a thickness of about ½- to ¾-inch (depending on how thick you like your English muffins. If using metric, 1.5cm is a good thickness). Cut out circles with a 3-inch (8cm) round cutter, and place on the sheet pan. Re-roll any excess and form more muffins. You should get 12-14 muffins total. Slide the muffins around on the semolina to ensure they don't stick to the pan.

Once shaped, cover the muffins with a clean towel and proof them at room temperature for 30 minutes to 1 hour, or until they’ve almost doubled in size.

Heat a flat pan, griddle, or cast iron skillet over medium heat. Once the pan is hot, use a thin spatula to transfer the muffins (in batches) from the sheet pan onto the skillet. Cook for 12 minutes, 6 minutes on each side, until firm and golden brown. Turn only once. Repeat with the remaining muffins.

Once cool enough to handle, use a fork to break the muffins apart. This fork method ensures you get nooks and crannies! Toast your muffin if desired, and enjoy with butter and/or jam!