Step 1
Using a wooden spoon or rubber spatula, mix 4 cups (500 g) all-purpose flour, 1 Tbsp. Diamond Crystal or 1¾ tsp. Morton kosher salt, one ¼-oz. envelope instant yeast (about 2¼ tsp.), and 1¾ cups warm water in a large bowl just until flour is hydrated and a very shaggy dough forms, about 1 minute. Cover bowl with plastic wrap and let mixture sit at room temperature 15 minutes.
Step 2
Set a small bowl of room-temperature water on work surface for easy reaching. Uncover dough and, using a damp hand, stretch one side of dough up and over to meet opposite side; turn bowl 90°. Repeat process 3 more times, turning bowl after each fold. (This constitutes 1 full fold.) If dough doesn’t always stretch to meet opposite side, just aim for the middle. Re-moisten your hands and shake off excess water any time dough begins to feel sticky. Cover dough and let sit 30 minutes (set a timer). Repeat folding process to make 1 full fold every 30 minutes, for a total of 3 more full folds, 1 hour and 30 minutes total. By the last full fold, the dough should be significantly smoother and tighter.
Step 3
Add about half of 4 jalapeños, halved lengthwise, cut into ½” pieces, and one 8-oz. block sharp orange cheddar, cut into ½” cubes, to dough, pressing pieces in, then stretch dough over itself to evenly distribute throughout. Repeat with remaining jalapeños and cheddar. (You don’t need to be precise; some pieces will fall out.)
Step 4
Transfer dough to a generously floured surface, dust with flour, and shape into a tight round ball by cupping dough with your hands and pulling it toward you. (There should not be a ton of pieces of jalapeño or cheddar popping out; try to keep them inside as much as possible.) Dust dough with more flour. Dust a kitchen towel with flour and place in a high-sided bowl to line. Place dough, smooth side down (seam side up), on top of towel in bowl. Tightly cover bowl with plastic wrap. Let dough sit in a warm, dry spot until puffy, about 45 minutes.
Step 5
Place a rack in middle of oven and set a large Dutch oven with a lid in center of rack. Preheat to 450°.
Step 6
Place a 12×12″ sheet of parchment paper on surface. Cut a 2″ slit in each corner, cutting toward the center (this should create a sling of sorts); place on a large plate. Set parchment-lined plate upside down over bowl and very carefully turn bowl and plate over in one motion to tip dough out gently onto center of parchment (try your best not to deflate or ruin its shape). Working very quickly and using a pair of sharp scissors lightly coated in vegetable oil, cut an X in center of dough. Using parchment paper, very carefully lower dough on parchment into center of Dutch oven. Cover pot and bake bread 35 minutes.
Step 7
Remove lid from pot and reduce oven temperature to 375°. Continue to bake bread until crust is deeply browned, 60–90 minutes more. Carefully turn loaf out onto a wire rack and let cool before slicing (about 2 hours).