Melt butter in a large saucepan over medium heat. Saute onion and garlic for 3 minutes.
Stir in milk and cook for 2 minutes, stirring occasionally.
Stir in tomato puree and sugar. Mix well, cover and bring to a boil over high heat.
Reduce heat to low and simmer, covered, for 5 minutes.
Add spinach, basil, salt and pepper and simmer, uncovered, for 2 minutes, stirring occasionally.
Sprinkle with parmesan cheese, if desired.
4 servings