While the tomatillos are baking, prepare the beef and rice soup.
Heat 1 tablespoon neutral cooking oil in a large soup pot over medium-high heat until very hot. Add the diced onion and cook, stirring often, for 6-8 minutes until beginning to soften and turn golden brown.
Add the beef and cook for 10-12 minutes, breaking the beef up with a spoon as it cooks.
Season the beef and onions with chili powder, cumin, cayenne powder, paprika, coriander, and the ground celery seed, if using. Season to taste with salt and pepper. Cook an additional 5-7 minutes or until fond begins to develop on the bottom of the pot.