Preheat the oven to 350°F .
Add the ground beef, Parmesan, Italian cheese, breadcrumbs, egg, salt, pepper, garlic powder and onion powder to a large bowl. Gently mix everything together until just combined.
Form the mixture into evenly sized meatballs and place them onto a parchment paper lined baking sheet. Bake for about 30 minutes, or until the meatballs are cooked through and reach an internal temperature of 160°F.
While the meatballs are baking, melt the butter in a large skillet over medium heat and sauté the garlic for about 30 seconds to 1 minute. Add the chicken broth, heavy cream, Parmesan, salt, pepper, garlic powder, Italian seasoning and Dijon mustard. Stir everything together until well combined.
Stir in the diced sun-dried tomatoes and baby spinach. Once the spinach has wilted, lower the heat and let the sauce gently simmer for about 5 minutes, stirring occasionally, until it begins to thicken.
Add the cooked meatballs to the skillet and gently toss them in the sauce. Let everything simmer together for another 5 minutes, then serve warm.