Preheat oven to 325℉. Begin by infusing the cream for the potatoes. Add heavy cream, garlic, 1 sprig rosemary, salt, pepper, and nutmeg to a medium saucepan. Bring to a simmer over medium to medium-high heat. Once simmering, reduce heat to medium-low and let steep for 10 minutes. Remove from heat.

Grease a heavy bottomed oven safe skillet (preferably cast iron) with the softened butter. Arrange 1/3 of the potatoes in an even layer on the bottom of the skillet, followed by 1/3 of the Gruyere cheese. Repeat with remaining potatoes and Gruyere, with the final layer of Gruyere on the top. Pour the cream over the top (I like to leave the garlic cloves and rosemary in there for extra flavor!). Sprinkle with the parmesan cheese. Lay the remaining 2 sprigs of rosemary on top. Cover tightly with aluminum foil and bake for 1 hour, or until potatoes are tender.

Meanwhile, make the rosemary pecan crunch. Heat a medium nonstick skillet over medium-high heat. Add the pecans, brown sugar, maple syrup, olive oil, salt, and cinnamon and cook for 3-4 minutes, stirring frequently, or until sugar has melted and caramelized, and pecans are golden brown and fragrant. To finish, stir in the rosemary and an extra pinch of salt. Let cool.

Once gratin has baked for an hour, remove the foil and preheat your broiler to high. Carefully position the rack in the upper third of the oven. Broil gratin for a few minutes, until the top is golden brown and bubbly. Let cool for a few minutes, then sprinkle the top with maple rosemary pecan crunch. Serve hot!