In large skillet over medium heat, sauté well drained spinach until heated through and all liquid is evaporated. Remove from skillet.
Add butter to skillet; when melted add onion and garlic; salt and pepper to taste. Sauté until onions are tender (about 3-5 minutes).
Whisk in flour; cook 1 minute. Whisk in half & half and nutmeg; bring to a simmer, whisking constantly. Simmer until thickened and reduced slightly (about 2 minutes).
Stir in spinach and cheese; continue cooking until heated through.