In the bowl of a stand mixer fitted with the dough hook attachment, stir melted butter, sugar, and warm milk together until sugar is dissolved (I stirred this by hand with a spoon, not with the dough hook). Add yeast and beaten egg and stir to combine.
Sprinkle the flour over the top of the milk mixture, followed by the salt and baking powder/water mixture. Knead with the dough hook until a sticky, elastic dough forms, being sure to scrape the sides and bottom of the bowl. Dough is meant to be loose and sticky; you may be tempted to add more flour, but don't.
Cover the bowl with a kitchen towel and allow to rise in a warm place for 90 minutes - 2 hours. The dough should be well-risen and full of air bubbles.
Heat a large skillet over medium heat. Have a biscuit cutter ready.
Preheat oven to 400 and have a sheet pan ready.
Dust your work surface generously with cornmeal and flour. Gently pour your risen dough onto the work surface, being careful not to knead or stir. Dust top of dough with cornmeal/flour until it's not sticky. Gently pat the dough out into a circle about 1-1.5 inch thickness. Use the biscuit cutter to cut your muffins. Carefully pick them up and place them promptly into the hot skillet.
When the muffins are golden and firm on the bottom, after 2-3 minutes, flip. Cook another 2-3 minutes, then transfer them to the baking sheet. Continue cooking muffins in batches.
Finish the muffins in the oven for 5 minutes. Remove to a cooling rack.
Split with a fork (if you use a knife you won't get the same nook and crannies effect). Store in a bag.