In a saucepan, melt butter over medium-high heat. Whisk in flour and cook 2–3 minutes until golden. Whisk in milk, season with salt and pepper, then refrigerate the mixture.
In a stockpot, brown the ground beef over medium-high heat. Season with salt, pepper, and garlic powder. Transfer beef to a plate, leaving 2 tablespoons of fat in the pot.
Add onion, potatoes, and bell pepper to the pot. Cook 10–12 minutes until softened and fork-tender.
Season with cumin and cayenne. Add corn, black beans, and green chiles.
Return beef to the pot. Pour in broth, bring to a boil, then reduce heat and simmer 15 minutes.
Stir in the chilled roux mixture. Add Velveeta, cover, and cook 15 minutes until cheese is melted and soup is thick and smooth.
Serve hot topped with grated cheddar and bacon bits.
Notes
Simmer long enough for the potatoes to soften fully and the cheese to melt smoothly.