The evening before you want to make the muffins, place the mature sourdough starter, milk, syrup, flour, and salt in the bowl of a stand mixer.
Attach the dough hook to the mixer and mix the ingredients on low speed. Alternatively, this could be done by hand.
Cover the bowl and set aside for a half hour. When the time is up, knead the dough with the dough hook for another five minutes.
Cover the bowl again and set aside for 10-14 hours.
When that time is up, the dough should be nice a puffy. Turn it out onto a lightly floured surface.
Using your hands, press the dough into a flat disk about ½ inch thick. Use a wide mouth glass to cut out each muffin. When you run out of space. Reform the remaining dough into a disk.
Set the muffins aside and sprinkle cornmeal on both sides. Cover them with a clean dish towel for about an hour.
Heat a skillet on low heat. Then place half of the muffins in the skillet and cook for about four minutes or until golden brown on one side.
Flip the muffins over and cook the other side for another four minutes. When they are golden brown on both sides (or 200°F in the center), set them aside on a cooling rack and repeat with the rest of the muffins.