Combine potatoes, broth, and salt in a multi-functional pressure cooker (such as Instant Pot). Close and lock the lid. Select high pressure according to manufacturer's instructions; set the timer for 1 minute. Allow 10 to 15 minutes for pressure to build.

Release pressure carefully using the quick-release method according to manufacturer's instructions, about 5 minutes. Unlock and remove the lid. Transfer potatoes to a deep 8-inch square baking dish.

Stir 1 1/2 cups Cheddar cheese, cream, garlic powder, black pepper, and nutmeg into the remaining liquid in the Instant Pot. Select the Sauté function; cook until smooth and creamy, about 5 minutes.

Meanwhile, set an oven rack about 6 inches from the heat source and preheat the oven's broiler.

Pour cheese sauce over potatoes: sprinkle with remaining 1/2 cup Cheddar cheese.

Broil in the preheated oven until cheese is golden, about 5 minutes.