Wipe the chiles with damp paper towel to remove any dust and cut them open.
Remove the stems, seeds, and veins.
In a dry skillet, over medium heat, toast the chiles until aromatic, about 6 to 8 seconds on each side.
Put the chiles in a bowl and barely cover with hot water.
Soak for 20 minutes.
Transfer the chiles to a blender and discard the water.
Add the garlic and chicken broth.
Blend for 1 minute to a smooth purée.
Add the cream, salt, and pepper.
Pulse just to mix.
Reserve in the blender jar.
Preheat the oven to 375°.
Brush an 8-inch-square baking dish with vegetable oil.
Arrange the sliced potatoes in the dish.
Pour the chile mixture evenly over the potatoes.
Bake uncovered until the potatoes are tender, and the sauce is bubbling, about 45 minutes.