Coat the bottom of a large stockpot with extra virgin olive oil. Add diced onions and minced garlic and toss in the olive oil until coated. Set the pot to medium heat. Once the garlic and onions start to sizzle and soften, add the diced sweet peppers and stir to combine. Allow this mixture to soften, 2-3 minutes.
Add tomato puree, dry spices, salt, pepper and sugar. Stir until combined. Lower heat to a simmer.
Peel the casing off the sausage links and break into bite-sized pieces. Drop the pieces into the gravy. Cover and simmer for at least 2 hours, occasionally stirring gently.
Bring a large pot of salted water to a boil. Cook the pasta according to package directions for al dente pasta. Drain.
Preheat oven to 375 degrees.
In a large bowl, combine the ricotta, egg and 1 cup of shredded mozzarella. Add 3-4 cups of tomato gravy and sausage, depending on how saucy you like it. Add the cooked pasta.
Pour the entire thing into a 9x13 baking dish. Dot with additional spoonfuls of gravy and sprinkle the remaining mozzarella over top. Bake for 20 minutes, until cheese is melted.