Preheat the oven to 375 degrees. Cut the French bread in half lengthwise. Pull out some of the bread from the center of one half of the loaf; make sure to not go all the way through. Keep the other half for another use. Place onto a baking sheet, place into the oven and bake until lightly toasted (about 2 minutes).
Heat olive oil in a large skillet over medium-high heat. Add the ground beef and cook until browned. Drain off any excess liquid. Add onion and garlic and cook for 2 minutes. Add the tomato paste, tomato sauce, thyme, and oregano. Season with salt and pepper. Mix well. Reduce heat and simmer for 20 minutes.
In a large bowl combine the ricotta cheese, parmesan cheese, egg yolk, and parsley. Season with salt and pepper. Mix well.
Spread the ricotta mixture over the toasted French bread. Top with the meat sauce mixture and then with a layer of shredded mozzarella cheese. Place into the oven and bake for 15-18 minutes or until golden and bubbly. Top with fresh basil if desired.