Step 1: In a large skillet or pot, wilt the fresh spinach in batches over medium heat with a tablespoon of water or a small pat of butter. Once wilted, transfer to a colander.
Step 2: Press the spinach firmly with a spoon or squeeze it in a clean kitchen towel to remove as much excess water as possible. Roughly chop the spinach and set aside.
Step 3: In the same skillet, melt the 3 tablespoons of butter over medium heat. Add the minced shallot and cook for 2-3 minutes until soft.
Step 4: Add the minced garlic and cook for another 1 minute until fragrant. Sprinkle the flour over the butter and aromatics, whisking for 1 minute to cook out the raw flour taste.
Step 5: Gradually pour in the heavy cream while whisking constantly. Simmer for 3-5 minutes until the sauce has thickened significantly.
Step 6: Stir in the Parmesan cheese, nutmeg, salt, and pepper. Once the cheese is melted, fold in the prepared spinach.
Step 7: Cook for another 1-2 minutes until everything is heated through. Adjust seasonings to taste and serve immediately.