Combine the ingredients in a mixing bowl and stir until it forms a thick batter. Cover with a clean towel or plastic wrap and let sit at room temperature for 12 hours.
After 12 hours, it should be very bubbly. If not, let it sit for a couple more hours. If it still isn’t bubbly, your starter is not active enough and you’ll need to feed it another day or two.
Make the dough:
When your leaven is ready, add it to a mixing bowl with the warm water water. Mix until the leaven is fully mixed with the water.
Add the salt, flour, 1 cup cheddar, and Parmesan cheese. Stir with a wooden spoon until you have a very shaggy dough.
Cover with a clean towel and let rest for 2-4 hours.
Fold the dough by lifting one side of the dough and folding over itself. After each fold, turn your bowl, and fold four times. Let the dough rest for a half hour, then fold again. Repeat this process four times, resting for a half hour between each one.
After folding, form the dough into a ball. Let rise for 3-4 hours. Form into a tight ball and place on parchment.
After forming the dough into a ball, place a large Dutch oven in the oven and preheat to 450 degrees.
When done resting, carefully remove the Dutch oven and lift the parchment with the dough into the pot. Using a sharp knife, make an X on top of the loaf.
Put the lid on and return to the oven.
Bake for 30 minutes. Remove from oven, remove lid.
Sprinkle the remaining cheddar on top of the loaf.
Put back in the oven without the lid. Continue baking for 30-40 minutes until crust is dark golden brown and cheese is browned.
Carefully remove the bread from the pot and cool on a rack.