Preheat and prepare
Preheat your oven to 425°F (about 220°C). Line a baking sheet with parchment paper for easy cleanup.

Mix the meatball mixture
In a large mixing bowl, combine the ground beef and ground veal with the breadcrumbs, beaten eggs, ricotta cheese, grated onion, minced garlic, grated Parmesan, kosher salt, pepper, and dried Italian seasoning. Mix thoroughly until all ingredients are evenly incorporated. Ensure there are no pockets of unmixed ingredients, so each meatball cooks evenly.

Form and oil the meatballs
Divide the mixture into eight equal portions. Shape each portion into a large meatball and place them on the prepared baking sheet. Drizzle the 2 tablespoons of olive oil over the meatballs so they brown nicely in the oven.

First bake
Place the baking sheet in the preheated oven. Roast for 15–20 minutes, or until the outsides begin to brown.

Lower heat and continue baking
Lower the oven temperature to 375°F (about 190°C). Continue baking the meatballs until their internal temperature reaches 145°F (about 63°C), which should take another 18–24 minutes.

Prepare the sauce while meatballs bake
While the meatballs are baking, warm 2 tablespoons olive oil in a large oven-safe skillet or braiser over medium heat. Add the finely grated onion and thinly sliced garlic. Sauté until the garlic begins to brown, about 4–6 minutes. Reduce heat as necessary so the garlic does not burn. Add red pepper flakes, freshly ground black pepper, kosher salt, crushed tomatoes, and basil leaves. Stir to combine, bring to a gentle boil, then reduce heat and simmer the sauce for 15 minutes.

Combine meatballs with sauce
After the meatballs have baked and reached 145°F, transfer them gently into the simmering tomato basil sauce in the skillet. Spoon sauce over each meatball to ensure they are coated.

Final bake to finish cooking
Return the skillet (or transfer to an oven-safe dish) to the oven and bake until the internal temperature of the meatballs reaches 160°F (about 71°C). This should take roughly 10–12 minutes. After baking, remove the basil leaves. Optionally top with freshly grated Parmesan cheese before serving.