In a large saucepot over medium heat, heat the heavy cream and the garlic. Steep for 5 minutes to allow the garlic to permeate the cream. Once a low simmer is reached, begin slowly whisking in the cheese until it melts and is fully incorporated. Taste and season with a pinch of salt and plenty of black pepper. Keep warm.
In batches, add spinach to the sauce and stir, allowing the heat to wilt the spinach. Cook while stirring to allow the moisture to evaporate from the spinach.