Add the starter, water, fermented jalapenos and juice, and flour to the bowl of a stand mixer fitted with a dough hook. Mix on low speed until the ingredients are just combined. (You can also mix by hand.)
Let the dough rest for 10 minutes. Sprinkle in the salt. Mix on low speed for 3 minutes. (If mixing by hand, stir the dough with a wooden spoon for 3 minutes.)
Cover the dough in the bowl with a clean kitchen towel. Let it sit for 5 hours at room temperature (about 70°F).
After 5 hours, the dough should be doubled in size and moist and sticky. If it has not doubled, then let rise until it does double. Stir the dough down with a couple of turns of your mixer or with your wooden spoon, and then roll it out on a lightly floured surface.
Fold the edges of the dough to the middle to roughly shape it into a ball. Dust the dough with flour, and using the fingertips of both hands, continue folding the outer edges of the dough to the middle until you have a ball. Don’t use large amounts of flour to dust the dough, but keep enough flour on the dough to prevent it from sticking to your hands.
To make a round boule shape, place your hands on opposite sides of the dough, making sure you have some flour on the surface so your hands don’t stick. Turn the boule in a counterclockwise direction, shaking it gently from side to side at the same time to encourage the dough to shape up from its flat state into a more tightly wound ball. Three or four turns should form a round ball. It doesn’t have to be exact.
Grease an 8-inch round glass or ceramic baking dish and sprinkle it with a bit of cornmeal. Place your boule in the center of the dish and sprinkle its surface with a little cornmeal, too. Cover the dough with a clean, damp kitchen towel.
Let the boule rise for about 2½ hours, or until doubled in size.
Make sure your oven is preheated to 450°F when the dough is ready.
Slash the top of the dough two or three times with a sharp knife before placing it in the oven. Bake at 450°F for 5 minutes, then reduce the heat to 425°F. Bake the bread for another 25 minutes, turning the loaf halfway for even browning.
Remove the bread from the pan and transfer it to a wire rack to cool.