Melt the butter in a large skillet over medium heat. The butter should loosen and lightly foam without browning hard or smelling toasted.

Add the sliced shallot and minced garlic, then cook until the shallot turns translucent, about 2 minutes. You want a soft, fragrant base here, with the garlic smelling mellow and not scorched.

Lower the heat to medium low and add the heavy whipping cream, cream cheese, black pepper, and grated parmesan, stirring with a silicone spatula until smooth. Keep stirring until the cream cheese fully disappears into the sauce and the mixture looks creamy rather than broken.

Add the spinach and fold it into the sauce until it is slightly wilted. The greens should shrink, turn a vivid deep green, and look coated instead of swimming in liquid.

Taste, add salt if you want it, and serve right away. Wait until the end because the parmesan already brings salt, and the finished dish should taste rich and balanced rather than sharp.