Preheat the oven to 400°F (200°C). Spray at least 2-inch deep large casserole dish with cooking spray.
Cut the potatoes into 1/8-inch thin slices.
In a medium bowl, whisk together ½ cup of heavy cream, flour, garlic, salt and pepper until well combined.
Stir in the remaining heavy cream, milk and cilantro.
Arrange half of the potatoes in prepared baking dish.
Pour half of the cream mixture over the potatoes.
Sprinkle half of each cheeses in even layer.
Layer the remaining potato slices, pour the remaining cream mixture and sprinkle the cheeses.
Cover with foil and bake for 30 minutes.
Remove the foil and bake another 20 minutes, or until the potatoes are fork-tender. If desired, broil for about 2 minutes for beautiful golden color.
Let it rest for 10-15 minutes before serving.