Thaw the spinach completely and squeeze out as much liquid as possible so the finished dish stays rich and creamy rather than watery.

Melt the butter in a large skillet over medium heat. Add the shallot and cook until softened, then stir in the garlic and cook briefly until fragrant.

Sprinkle the flour over the shallot mixture and cook briefly, stirring constantly.

Slowly whisk in the milk followed by the heavy cream until smooth.

Cook gently, stirring frequently, until the sauce begins to thicken.

Stir in the Parmesan, cream cheese, nutmeg, salt, black pepper and crushed red pepper flakes, if using.

Fold the well-drained spinach into the cream sauce until evenly coated.

Cook gently until the spinach is completely heated through and the sauce is thick and creamy. Taste and adjust the seasoning as needed.

Transfer to a warm serving dish and finish with Parmesan, freshly cracked black pepper and parsley if desired.