Preheat your oven to 375°F (190°C). Lightly grease your non-stick 9x13-inch pan with a tiny bit of butter.

Melt 2 tablespoons of butter in a skillet over medium heat. Add the sliced leeks and a pinch of salt. Cook for 6 to 8 minutes until soft, sweet, and translucent. Remove from heat.

In a small saucepan over medium-low heat, gently warm the heavy cream.

Crumble the entire wheel of Boursin cheese into the warm cream. Whisk continuously for 2 to 3 minutes until the Boursin is completely melted and the sauce is smooth and velvety. Remove from heat.

Arrange half of your thin potato slices in the bottom of the non-stick pan.

Scatter all of the sautéed leeks evenly over the first layer of potatoes.

Layer the remaining potato slices on top.

Season the top layer with salt and black pepper, then pour the warm Boursin cream sauce evenly over everything.

Sprinkle all of the aged white cheddar and half of the Grana Padano evenly over the top.

Cover the pan tightly with aluminum foil.

Bake for 35 to 40 minutes until the potatoes are tender when pierced with a fork.

While baking, mix the Panko breadcrumbs, 2 tablespoons of melted butter, and the remaining Grana Padano together in a small bowl.

Remove the foil from the pan (watch out for steam).

Scatter the buttery Panko mixture evenly over the melted cheese layer.

Return the pan to the oven uncovered and bake for another 15 minutes, or until the Panko topping is deeply golden brown and ultra-crispy. Let it rest for 10 minutes before slicing so the sauce sets.