Combine ricotta, red pepper flakes, basil leaves in a small bowl until completely mixed. Add salt & pepper to taste. Set aside.
In a large skillet with a lid over medium heat, add olive oil. When hot, add Italian sausage and cook until crumbled and just starting to brown, about 5-8 minutes.
Add onion, garlic, and Italian seasoning, and cook until onion just starts to soften, about 5 minutes.
Add crushed tomatoes, chicken stock, and pasta. Stir to combine. Use a large spoon to make sure all pasta is covered with the liquid. Increase heat to high so that the pasta comes to a boil, then reduce to low.
Cover and cook until pasta is tender (time depends upon what pasta you used) – usually 15-20 minutes.
Take off heat and place spoonfuls of the ricotta mixture on top of the cooked pasta. Sprinkle the shredded mozzarella over the surface of the whole dish.
Place uncovered under a broiler for about 5 minutes or until cheese is melted, golden, and bubbly. Remove from the oven and let sit for about 5 minutes to cool slightly.
Before serving, garnish with torn basil leaves and drizzle pesto over the whole dish.
Serve with a green salad for a complete dinner!