Step 1

Melt butter in a large skillet over medium heat.  Add onion and cook, stirring frequently, until onion is tender (about 3 to 4 minutes).

Step 2

Add garlic and cook until fragrant, stirring constantly (about 30 seconds).

Step 3

Add heavy cream, cream cheese, salt, pepper and nutmeg.  Stir until cheese is melted and mixture is smooth.

Step 4

In a bowl or large measuring cup, whisk together milk and flour.  Pour into mixture and stir to combine.

Step 5

Cook, stirring constantly, until thickened (about 3 minutes).

Step 6

Add spinach and stir well to combine.  Cook (stirring frequently) until spinach is heated, about 1 to 2 minutes. Season with additional salt and pepper, if desired.

Step 7

Sprinkle with freshly grated Parmesan, if desired.