Melt the butter in a large skillet over medium-low heat. Add the shallots and cook, stirring frequently, until soft and translucent, about 4 minutes.

Add the garlic and cook, stirring constantly, for 1 minute more. Do not brown.

Add the heavy cream, salt, pepper, and nutmeg and bring to a gentle boil.

Cook, uncovered, stirring occasionally, until the cream is thick enough to coat a wooden spoon, about 10 minutes.

Add the cheese and stir until melted.

Add the spinach and stir until evenly combined with the cream sauce. Taste and adjust seasoning if necessary.

If the spinach seems a little watery, cook over medium-low heat until any excess liquid evaporates. Serve warm.