Steak with Creamy Au Gratin

Ingredients

• 2 lbs Russet potatoes, peeled and thinly sliced (about 1/8 inch thick)
• 2 cups heavy cream
• 1 cup whole milk
• 2 cloves garlic, minced
• ½ tsp nutmeg, freshly grated
• 1 tsp salt, plus more for seasoning
• ½ tsp black pepper, freshly ground
• 2 tbsp unsalted butter
• 1½ cups Gruyère cheese, shredded
• ½ cup Parmesan cheese, freshly grated
• 2 (12 oz) Ribeye or New York Strip steaks, about 1 1/2 inches thick
• 2 tbsp olive oil
• 1 tbsp unsalted butter
• 2 sprigs fresh rosemary
• 2 cloves garlic, smashed
• 1 tsp coarse sea salt