Heat your oven to 350 degrees. Slice the tomatoes in half and arrange them in a single layer on a parchment lined baking sheet. Drizzle about 2 tablespoons of olive oil over the tomatoes, and then generously sprinkle with salt and freshly ground black pepper. Let roast for 45-50 minutes, until there is very little liquid on the bottom of the pan.

Pour the tomatoes and any juices into a blender and puree until smooth. Add the basil leaves and blend until combined.

Dice the onion. Pour the last tablespoon of olive oil into a sauce pan. Once the olive oil is hot, add the onion. Season it with salt and pepper. Once the onion is soft, add the garlic and let sauté for 2 minutes. Then add the ground beef. Use a wooden spoon to break the beef up into small pieces as it browns.

Once all of the beef has browned, pour in the pureed roasted tomatoes. Bring to a simmer. The sauce should already be thick enough and shouldn't need to reduce. Stir in the cheese, then taste the sauce and add more salt and pepper as necessary.

You can freeze this sauce if you like.