Heat olive oil over medium-high heat in a 6-quart soup pot. Add onions, jalapenos (if desired), and 2 teaspoons salt and cook until soft, 2 minutes. Add ground beef, chili powder, oregano, and garlic and cook, breaking up any clumps of meat with a spoon, for 5 minutes. Add tomatoes, beans, and 1/2 cup water; stir and bring chili to a boil. Reduce heat to a simmer and cook until thickened to chili consistency, about 20 minutes. Taste, and add 1 teaspoon salt, if needed.
Preheat oven to 400 degrees.
While the chili is simmering, cook macaroni according to package directions in boiling salted water, drain in a colander, rinse under cool running water, and set aside. Grate cheddar cheese and set aside.
Place a 9-by-13.5-inch or other 3-quart casserole dish on a baking sheet. Once chili has finished cooking, fold in the cooked macaroni and 1/3 of the cheddar cheese. Transfer chili mac to the baking dish and top with remaining cheese. Bake until heated through and cheese is melted, about 10 minutes. Remove from oven and let cool 5 minutes before serving. Serve each portion garnished with a dollop of sour cream, if desired.
Yield: 6 to 8 servings