Step 1: Bring a large pot of salted water to a boil and prepare an ice bath in a separate bowl.
Step 2: Blanch the fresh spinach in boiling water for 1 minute until wilted, then immediately transfer to the ice bath.
Step 3: Drain the spinach and use a clean kitchen towel to squeeze out as much liquid as possible until the spinach is very dry. Roughly chop the dry spinach.
Step 4: In a large skillet, melt the butter over medium heat. Add the minced shallots and cook for 3-4 minutes until soft.
Step 5: Add the garlic and cook for another 1 minute until fragrant. Sprinkle the flour over the butter mixture and whisk for 1-2 minutes to cook out the raw flour taste.
Step 6: Slowly pour in the heavy cream while whisking constantly. Simmer for 3-5 minutes until the sauce thickens and coats the back of a spoon.
Step 7: Stir in the nutmeg, salt, pepper, and Parmesan cheese until melted and smooth.
Step 8: Fold the chopped spinach into the cream sauce and cook for an additional 2 minutes until heated through. Serve immediately.