Begin by preparing the sloppy joe filling. In a large skillet, brown 1 lb of ground beef with 1 chopped onion and 2 minced garlic cloves over medium-high heat, breaking up the meat as it cooks. Once the beef is fully browned and the vegetables are softened, drain excess fat if necessary.
Stir in 1 (1 3/4 ounce) package of Manwich sloppy joe mix, 6 ounces of tomato paste, and 1 1/4 cups of water. Mix everything together thoroughly and simmer according to the Manwich package directions until the sauce reaches the desired consistency and flavors meld together.
While the meat mixture simmers, prepare the cornbread base. In a separate bowl, combine 1 (8 ounce) box of cornbread mix with 2 beaten eggs, 1/2 cup of melted butter, and 1/4 teaspoon of salt.
Fold in 1 (14 3/4 ounce) can of whole kernel corn (drained) and 1 (14 ounce) can of creamed corn until just combined. Pour this cornbread mixture into a prepared 9×13 inch casserole dish, spreading it evenly across the bottom.
Spread the cooked sloppy joe meat mixture over the cornbread layer, then top the entire casserole with 8 ounces of shredded monterey jack and cheddar cheese blend.
Place the casserole in a preheated 350°F oven and bake for approximately 45 minutes, until the cornbread at the edges begins to brown and the casserole is heated through. Remove from the oven and let rest briefly before serving.
