Preheat the oven to 350°F (175°C) and prepare the baking pan by lining it with aluminum foil.

In a food processor, combine graham crackers, granulated sugar, and fine sea salt. Pulse until fine crumbs, about 30-40 seconds. Add melted butter and pulse until combined. Press into the bottom of the prepared pan and bake for 10 minutes.

In a large bowl, mix sweet potato puree, sugar, eggs, milk, cream, bourbon or vanilla, salt, and spices until smooth. Pour over the cooled crust.

Bake the filling for 40 minutes or until set at the edges, with a slight wobble in the center. Allow to cool at room temperature for about an hour.

Beat egg whites and cream of tartar until soft peaks form, about 3-5 minutes.

In a saucepan, combine sugar, corn syrup, water, and a pinch of salt. Cook over medium heat until sugar dissolves; then bring to a boil. Cook until it reaches 240°F (115°C). Carefully pour hot syrup into beaten egg whites and beat until thick and glossy, about 5 minutes.

Spread the marshmallow topping over the cooled filling and create peaks. Toast using a kitchen torch or broil briefly in the oven, watching closely to prevent burning.

Chill the pie bars in the refrigerator for at least 1 hour before slicing.