Heat oven to 350 degrees F and adjust rack to middle position.
Melt the butter in a medium sauce pan over medium heat until foaming subsides. Add the onion and cook, stirring occasionally until soft and just turning golden brown, about 5-7 minutes. Add the garlic, salt and pepper and cook until fragrant, about 30 seconds. Pour in the broth and cream, then bring to a simmer.
Place half of the potatoes in an even layer in an 11×7-inch baking dish. Sprinkle with half of the cheese. Place the remaining potatoes on top in an even layer. Pour the hot cream mixture on top. Place a piece of parchment paper and then a piece of foil over the potatoes. Bake for 30 minutes. Remove the parchment and foil, sprinkle with the remaining cheese and bake for an additional 20 minutes, until brown, bubbly and potatoes are fork tender. Cool 10 minutes before serving.