Cook and drain spinach; set aside.
Season with salt and pepper to taste.
Sauté onion in olive oil until clear and tender; add to spinach.
Stir together milk and cream cheese in large pot over low heat until smooth.
Remove from heat.
Add spinach mixture and both cheeses.
Mix until well blended.
Place mixture into a casserole.
Dip may be refrigerated and reheated in microwave.
Serve dip with tostado chips, salsa, and sour cream if desired.Servings: 4