Brown the Stew Meat: Heat 2 tablespoons of olive oil in a large Dutch oven over medium heat for about 5 minutes. Add the stew meat and sauté for 10 minutes, or until the meat is browned on all sides. Remove the stew meat and set aside.
Sauté Vegetables: Add the remaining 2 tablespoons of olive oil to the Dutch oven and heat for 3 minutes over medium heat. Add the diced onions and green pepper, sautéing for 8 to 10 minutes until softened. Stir in the minced garlic and cook for 1 additional minute, until fragrant.
Cook the Ground Beef: Add the ground beef to the pot. Cook, breaking up large chunks with a spoon, for 10 to 12 minutes or until the beef is fully browned. Drain excess fat.
Combine Ingredients: Return the browned stew meat to the Dutch oven. Stir in the ground cumin, chili powder, onion powder, cayenne pepper, tomato paste, fresh diced plum tomatoes, canned diced tomatoes, beef base, and water.
Simmer: Bring the chili to a gentle simmer. Cover the pot and let it simmer over low heat for 3 hours, allowing the stew meat to become tender and flavorful.
Add Beans: Stir in the pinto beans and let the chili simmer for an additional 10 minutes, just until the beans are warmed through. Season with salt to taste.
Serve and Garnish: Ladle the chili into bowls and garnish with sour cream, shredded cheddar cheese, and diced tomatoes. Serve hot and enjoy!