Wash the spinach in several changes of water to get rid of any grit. Drain the spinach but keep some of the water clinging to the leaves. Heat the butter and oil in a large skillet over medium-high heat and add the spinach and garlic. Cook, turning frequently, until the spinach has wilted down evenly. Remove the garlic and put the spinach into a colander and let it drain well. Press out as much liquid as you can from the leaves and chop them coarsely.
Heat the skillet again over medium-high heat and add the cream and nutmeg; cook until it reduces a bit, about 5 minutes. Add the spinach and parmesan and season with salt and pepper. Cook until the spinach is hot, about 5 more minutes. Serve immediately.