Preheat your oven to 350°F and grease an 8x8-inch metal pan with foil. In a food processor, pulse together graham crackers, granulated sugar, fine sea salt, and melted unsalted butter until combined. Press this mixture firmly into the bottom of the pan, creating an even layer. Bake for 10 minutes until set and slightly golden.

In a large mixing bowl, combine fresh sweet potato puree, granulated sugar, eggs, whole milk, heavy cream, bourbon, fine sea salt, and ground spices. Beat until smooth and creamy. Once your crust has cooled, pour the sweet potato filling over it, then bake for 40 minutes.

While the filling cools, beat egg whites until soft peaks form. In a saucepan, combine sugar, corn syrup, water, and a pinch of salt. Simmer until it reaches 240°F.

Gradually drizzle the hot syrup into the whipped egg whites while continuing to beat at medium speed. Keep whipping until thick and glossy, forming stiff peaks. Fold in vanilla extract.

Once the sweet potato layer is cool, spread the marshmallow topping evenly across it. Use a kitchen torch to caramelize the marshmallow, or place it under the broiler for about a minute, watching closely to prevent burning.

Let the bars cool in the refrigerator for at least one hour before serving. Cut into squares to enjoy.