Creamy Tomato and Spinach Tortellini Soup

butter

onion (, diced)

garlic (, chopped)

red pepper flakes (, to taste)

flour

vegetable broth

can diced tomatoes

can tomato sauce

cheese tortellini ((the refrigerated kind))

freshly grated parmesan cheese

fresh spinach ((packed))

heavy cream ((or Greek yogurt))

salt and pepper

fresh chopped basil