Heat milk to 115F. Add the sugar and stir to dissolve. Add the butter and stir until melted. Transfer to a large mixing bowl.
Stir in the sourdough starter. Sprinkle instant yeast and stir.
Add one cup of flour and the salt, and mix thoroughly.
Add another cup of flour and mix by hand. The dough should be slightly sticky.
Turn the dough in a lightly floured work surface. Roll out 1/2" thick and cut into 3" circles. Collect the cut-offs, re-roll and cut.
Transfer to a baking sheet dusted with cornmeal. Turn each miffing in cornmeal.
Cover and let rise for 1 hour or until the muffins double in size.
Preheat a skillet or a griddle to medium-low heat with a tablespoon of butter and a tablespoon of cooking oil. Cook for about about 8 minutes per side or until the muffins are cooked through. I find they cook better if you cover the pan with a lid after you flip them.
Remove, split and toast. Leftover muffins can be frozen for later. Just thaw them and toast before consuming.