Heat a large skillet over medium-high heat. Add spinach and cook until wilted, stirring constantly. Remove from the skillet and drain in a colander. Try to squeeze out as much liquid as possible.
Melt the butter in the skillet over medium heat. Add garlic and onions; cook and stir until tender, about 5 minutes. Add the spinach and stir in the heavy cream. Sprinkle in the provolone cheese and stir to melt and coat the spinach. Once the provolone has melted, stir in the Parmesan cheese and continue to cook and stir until thickened. Season with salt and pepper and serve hot.