Bring large pot of salted water to boil.
Add rinsed spinach leaves in batches.
Cook 1-2 minutes until spinach is just wilted.
Drain & rinse with cold water, making sure to squeeze out excess water.
Meanwhile melt butter in skillet on stove top over medium heat.
Once melted add cornstarch to form roux. Then add onions & garlic and cook about 2-3 more minutes.
Add half & half, cream cheese, & parmesan cheese and stir till completely melted and creamy another 1-2 minutes.
Add salt & pepper to taste, & nutmeg.
Stir in wilted spinach, top with addition parmesan cheese & red chili pepper flakes if desired.