Cook the ground beef over medium heat. When nearing fully browned, add in the flour, garlic, chili powder, and cayenne pepper powder. Cook for 3 minutes, stirring often, until aromatic.
Add in the beef stock and increase the heat to bring the mix to a boil. Once boiling, reduce the heat to low and simmer until the mix is thickened (approximately 20 minutes).
Add salt and pepper to taste.
Prepare the taco building station
Warm the tacos shells and place the Mexican style shredded cheese, lettuce, tomato, onion, and sour cream out for self-service taco building.
Transfer the spicy beef into a serving bowl and place among the other ingredients.
Place additional chili powder in a small dish to allow for post-taco-build sprinkling for an extra burst of heat.