Preheat oven to 350°F. Spread 2 tablespoons butter in the bottom and sides of a large casserole dish or cast iron pan.
Heat olive oil in a large skillet, add onions and sauté on low heat for 20 to 30 minutes, or until the onions are caramelized.
In a saucepan, combine, cream, fresh thyme, garlic, paprika, ½ teaspoon salt, and nutmeg. Simmer on low heat for 20 to 30 minutes, for the cream to infuse and the flavors to develop. Add in half of the cheese; stirring until melted, about 1 minute.
Place the potatoes in the bottom of the prepared pan and season with remaining ½ teaspoon salt and black pepper. Spread the caramelized onions in between and on top of the potato slices. Pour the cheese sauce over the potatoes and cover with foil. Bake for 1 hour and 15 minutes. Remove the foil, sprinkle the remaining half of the gruyere cheese and continue to bake for another 15 minutes, or until the potatoes are fork tender when pierced with a fork.
Let cook for 10 minutes before serving. Garnish with chives. Enjoy!
