Heat 2 tablespoons of olive oil in a medium skillet.

Add the diced onion and minced garlic and cook over medium heat for 8 minutes, until softened.

Stir in the thyme and rosemary, then season with salt and pepper.

Transfer the mixture to a large bowl and cool for about 10 minutes.

Soak the bread pieces in milk in a small bowl for about 5 minutes, until absorbed.

Squeeze the milk from the bread and add the bread to the bowl with the onions.

Add the ground veal, egg, grated Parmigiano-Reggiano, salt, and pepper.

Mix with clean hands until well combined.

Scoop 1 1/2 tablespoon-sized balls from the veal mixture.

Stuff a cube of Fontina cheese into the center of each meatball and roll to enclose.

Transfer the meatballs to a rimmed baking sheet and refrigerate for 30 minutes.

Heat 2 tablespoons of olive oil in a large nonstick skillet.

Cook the meatballs in batches over moderately high heat for about 6 minutes, until browned all over.

Return the meatballs to the baking sheet.

Heat the remaining 1 tablespoon of olive oil in the same skillet.

Add the sliced garlic clove and cook over moderately high heat for about 3 minutes, until lightly golden.

Add the tomato paste and cook, stirring constantly, for 1 minute.

Add the diced tomatoes and bring to a simmer.

Add the meatballs and any accumulated pan juices to the tomato sauce.

Cover and cook over moderately low heat, turning the meatballs once, until they are cooked through, about 10 minutes.

Transfer the meatballs to bowls or plates using a slotted spoon.

Simmer the sauce over moderate heat for about 2 minutes, until slightly thickened.

Season the sauce with salt and pepper and pour over the meatballs.

Serve with crusty bread.