Pour spinach leaves into a colander. Rinse thoroughly with warm water.
Leave colander in sink so spinach can drain. After draining, place leaves in a clean towel and ring until dry. This will prevent water from getting into the Creamed Spinach. Continue with next steps.
Heat milk and cream in a small saucepan over moderate heat. Stir constantly with a whisk until warm.
Remove from heat. Set aside.
In a 3-quart saucepan, melt unsalted butter over low-medium heat. Add chopped onions. Stir continuously until softened (4-5 minutes).
Stir in minced garlic.
Add sifted flour. Whisk together for 3 minutes to form a roux.
Add warm milk and cream mixture in a fast stream. Simmer AND whisk constantly until thickened (3-5 minutes). Whisking prevents lumps from forming.
Stir in rinsed/dried spinach, cayenne pepper, nutmeg, salt and coarse ground black pepper to taste.
Simmer and stir constantly until spinach is limp (2-3 minutes).
Sprinkle with grated Parmesan cheese (optional).