Preheat oven to 400 degrees and grease a large casserole dish. The one I use is a 14.5" x 8.75" x 3".
In a large pot, heat 1 tbsp of oil over medium heat.
Dice the onions and sauté them in oil until soft.
Grate the carrot finely and add to onion. Sauté for only around 30 seconds.
Add the ground beef and sausage to the pan and cook until no longer pink.
Add the crushed tomatoes, tomato sauce, ½ tsp sea salt, ¼ tsp garlic powder, 1½ tbsp dried basil and pinch of red pepper flakes.
Stir ingredients together and let simmer for 15 minutes.
While the tomato sauce is simmering, mix together cream cheese, sour cream, 1 tbsp basil, 1 egg, 1 tsp sea salt, ½ tsp black pepper, ½ tsp garlic powder and 1 cup of the mozzarella shredded. Set aside.
Cook spaghetti al dente, drain and set aside.
Once spaghetti is cooked and the sauce has simmered for 15 minutes, use a large ladle to spread about 1 cup of the sauce mixture to the bottom of the dish. On top of that you'll add ½ the noodles, spread ½ the cream cheese mixture and top with ½ the remaining sauce and 1/2 the mozzarella cheese. Repeat with the other ½ of the noodles, remaining ½ of the cream cheese mixture and top with remaining sauce. Sprinkle the remaining mozzarella cheese on the very top.
Bake for 30-40 minutes. You can set the oven to broil for the last 3 minutes to toast the cheese on top. Just be sure to watch it closely so it doesn't burn.