To make the crust, preheat oven to 350 F. Line a 9x5-inch loaf pan with parchment paper, and then lightly grease paper with nonstick cooking spray.

In a small bowl, stir together graham cracker crumbs and enough butter to form sandy crumbs. I used homemade graham crackers, so I only needed 3 tablespoons of butter. If you use regular graham crackers, you may need more butter.

Press the graham cracker mixture into the bottom of the prepared pan.

Bake for 8-10 minutes, or until set and the edges of the crust are golden.

Cool the pan on a wire rack until it reaches room temperature, about 20 minutes.

While the crust is baking, line a rimmed baking sheet with parchment paper. Grease with nonstick cooking spray.

Drop scoops of marshmallow crème onto prepared baking sheet.

When the crust has finished baking, turn oven to 450 F.

Toast marshmallow until golden brown, about 4-5 minutes.

While the crust is cooling, prepare the custard.

Whisk together the egg yolks, 1/2 cup sugar, vanilla extract, and salt until well-combined.

Place the bowl over a pot of simmering water, making sure the bottom of the bowl does not touch the water.

Whisk until the egg mixture reaches 160 F, about 15 minutes.

Once the mixture is at temperature, place the bowl into a larger bowl of lukewarm water.

Let the bowl sit for about 5 minutes; then, replace the lukewarm water with cold water.

While the egg mixture is cooling, beat the cream and remaining 1/4 cup sugar until thick with an electric mixer until the cream holds stiff peaks.

Add 1/4 of the cream into the cooled custard, and gently fold cream in.

Using a spatula, gently fold the remaining cream into the custard.

Pour the custard mixture over the cooled crust.

Drop spoonfuls of the chocolate-hazelnut spread and plops of the toasted marshmallow over the custard mixture; gently swirl to incorporate.

Cover with plastic wrap, and freeze for at least 8 hours or up to 3 days.

Serve in scoops or slices.