Stir the beans, tomatoes, onion, bell pepper, garlic, chili powder, cumin, broth and salt in a 6-quart crockpot.
Cover and cook on low for 5 1/2 hours until the vegetables are soft and the chili is bubbling at the edges.
Whisk the cornmeal, flour, baking powder and baking soda in a bowl, then stir in the egg, buttermilk and butter just until no dry flour remains.
Switch the crockpot to high and drop 8 equal mounds of batter over the chili, leaving narrow gaps for steam.
Cover without opening for 60 to 75 minutes until the dumpling centers reach 200°F and a toothpick comes out without wet batter.