Heat olive oil in a large pot over medium-high heat. Add ground beef and cook for 3-4 minutes, breaking it apart with a spoon as it cooks, until it's no longer pink and beginning to brown. Transfer the cooked beef to a plate, leaving about 1.5 tablespoons of the rendered fat in the pot—this flavorful fat will be your cooking base. While the beef cooks, prepare your aromatics: finely dice the onion into 1/4-inch pieces, slice the celery into 1/2-inch half-moons, peel and slice the carrots into 1/4-inch rounds, and mince the garlic. Having everything prepped and ready (mise en place) means you can move quickly through the next steps without stopping.

With the pot still over medium heat and the reserved beef fat as your base, add the diced onion, sliced celery, and sliced carrots. Cook for 7-8 minutes, stirring occasionally, until the vegetables begin to soften and the onions become translucent. This is where the magic happens—these vegetables are developing deep, caramelized flavors that will form the soul of your soup. In the final minute, add the minced garlic and cook for about 1 minute, stirring constantly, until fragrant. I like to let the vegetables get a little color on them rather than keeping them completely pale—it adds more depth to the broth.

Pour in the chicken broth, diced tomatoes with their juices, and tomato sauce. Add the cooked ground beef from Step 1 back into the pot. Sprinkle in the Italian seasoning and red pepper flakes, then season with salt to taste. Stir everything together to combine, ensuring the spices are evenly distributed throughout the liquid. Increase the heat to medium-high and bring the soup to a gentle simmer.

Once the soup reaches a simmer, reduce the heat to medium or medium-low and cover the pot partially with a lid. Let it simmer gently for 15 minutes, which allows the flavors to meld together and deepens the overall taste profile. You'll notice the broth becoming richer and more flavorful as the vegetables continue to break down slightly. I find that this brief simmering time is crucial—it transforms what could be a one-dimensional soup into something with real complexity.

Add the cheese tortellini directly to the simmering soup and stir gently to separate any that might be stuck together. Return the soup to a gentle simmer and cook for 4-7 minutes, depending on whether you're using fresh or frozen tortellini—fresh tortellini typically takes 4-5 minutes, while frozen may take the full 7 minutes. The tortellini is done when it floats to the surface and feels tender when tested with a fork.

Remove the pot from heat and stir in the fresh spinach and chopped parsley. The residual heat will gently wilt the spinach in about 1-2 minutes, preserving its bright color and fresh flavor. Give the soup a final stir and taste for seasoning, adjusting salt and red pepper flakes as needed. Ladle into bowls and serve immediately while the flavors are vibrant and the tortellini are still at their best.