Creamy Tortellini Soup with Spinach

For the soup:

• 2 tablespoons butter salted
• 1 cup yellow onion chopped (~1 small onion)
• 1 pound Italian sausage (bulk...without casing)
• 5 cups chicken broth or vegetable broth
• 1 ½ cup half-and-half
• 15 ounces diced tomatoes (1 can, with juice)
• 1 teaspoon oregano dried
• 1 teaspoon garlic powder
• ½ teaspoon black pepper
• ½ teaspoon salt
• 5 ounces spinach fresh baby
• 19 ounces cheese tortellini not dry, refrigerated or frozen, ~5 cups
• 2 tablespoons basil fresh

Optional garnishes:

• Parmesan Cheese shredded
• parsley chopped