Melt 1 tablespoon of butter to a large skillet set over medium-high heat. Add ground beef and break up with a spatula, then season generously with salt and pepper.
Cook ground beef until no longer pink, about 5-7 minutes. Transfer to a paper towel-lined plate.
Reduce heat to medium-low and melt remaining 2 tablespoons of butter in the skillet. Add chopped onions and cook until soft and translucent, 4-5 minutes. Add minced garlic and cook for 1 minute.
Add ground beef back to the skillet along with the kidney beans, diced tomatoes, chili powder, cumin, salt and pepper. Cook over medium heat, stirring often, for about 20 minutes or until chili has thickened slightly.
Chili can be made up to 5 days ahead. Store in the fridge.
To assemble nachos, preheat oven to 450°F.
Spread half of tortilla chips out onto a large sheet pan and cover with half of the cheese. Repeat with another layer of chips and cheese.
Bake just until cheese is melted and bubbly, about 5 minutes. Watch carefully so it doesn’t burn.
Remove nachos from the oven and top with warm chili. Add some sour cream, chopped scallions, and cilantro. Serve immediately.