In a large mixing bowl, whisk together flour, salt and yeast. Fold in the cheese and jalapeño until well coated. Add the water and stir until a shaggy mixture forms (mixture will be loose and sticky; this is what you want). Cover bowl with plastic wrap and set aside for 12 - 18 hours (up to 24). Overnight works great.
Preheat oven to 450. Place a cast iron dutch oven with a lid in the oven and heat the pot for 30 minutes. Meanwhile, transfer the risen dough onto a heavily floured surface (mixture will be sticky; do not knead) and lightly, gently shape into a round loaf.
Remove the hot pot from the oven, remove the lid, and carefully set the dough inside. Cover the Dutch oven and return it to oven for 30 minutes. Then, remove the lid, sprinkle the top of the loaf with grated cheddar and jalapeño slices, and bake an additional 10-15 minutes until golden and crisp. Carefully remove the pot from the oven and place the loaf on a cooling rack to cool. Best enjoyed warm, fresh from the oven.