In a large bowl, combine the active sourdough starter and warm milk.
Add sugar and mix until dissolved.
Gradually stir in the flour, salt, and baking soda.
Knead the dough on a floured surface for about 5 minutes until smooth.
Form the dough into a ball and place it in a greased bowl.
Cover and let it rise in a warm place for about 1 hour, or until doubled in size.
Punch down the dough and roll it out to about 1-inch thickness.
Cut out rounds using a biscuit cutter or glass.
Dust the tops with cornmeal and let the rounds rest for 30 minutes.
Heat a skillet over medium heat and cook muffins for about 7-8 minutes on each side until golden brown.