* Methods :
Preheat the oven to 325 degrees Fahrenheit in a small saucepan add the cream, salt and garlic. Simmer for 5 minutes. This will allow garlic flavor to soak the cream. Remove from the heat and adjust to the side.
Slice the potatoes thinly 1/8 inch thick using the mandolin slice.
In a 12-inch cast iron pan, add the butter and shallots and fry over a low heat for 5 minutes until the shallots are caramelized.
Arrange potato slices in a spiral pattern over cooked leeks. Pour cream mixture on the potatoes.
Cover the cast iron frying pan tightly with a piece of foil. Put the cast iron pan in the oven and bake for 1 hour 15 minutes. Remove the pan from the oven and turn the oven temperature until grilled.
Cover potatoes with Gruyere and Parmesan grated cheese. Spray thyme. Place the cast iron pan in the oven and grill for 5 minutes until the cheese is crispy and bubbles.
Remove from the oven and serve warm. It can be stored in the fridge and reheated the next day.
Enjoy !