Baked Penne and Cheese with Spinach

1 lb. Italian sausage , casings removed 1 medium onion , chopped 3 large garlic cloves, chopped 1 28-ounce can diced peeled tomatoes 1/4 cup pesto sauce 1 lb.[...]

2 teaspoons olive oil 1 cup onion , finely chopped (1 medium onion) 1 lb Italian sausage , hot (or mild if you prefer) 3 large garlic cloves , minced 1/2 cup[...]

3 cups penne or 3 cups other tubular pasta 6 ounces fresh baby spinach leaves, washed,uncooked 4 tablespoons butter 1 medium onion , chopped 1 lb sliced[...]