Special equipment: A 9-inch pie plate or a 10-inch tart pan with removable bottom; a 9-by-12-inch jelly roll pan or a 9-by-12-inch glass baking dish; kitchen shears and kitchen torch, optional
For the bourbon marshmallows: Spray a 9-by-12 inch jelly roll pan or glass baking dish with cooking spray. Sprinkle 1/2 cup of the confectioners' sugar on the pan and shake around to coat generously.
Pour 1/2 cup of the bourbon in the bowl of a stand mixer fitted with the whisk attachment. Sprinkle the gelatin over the top and turn the mixer on low speed while you make the syrup.
Put 1/4 cup water and the remaining 1/4 cup bourbon in a medium saucepan. Add the granulated sugar and corn syrup. Bring to a boil over medium- high heat and cook until the syrup reaches 240 degrees F. on a candy thermometer.
With the mixer on low speed, pour the sugar syrup down the sides of the mixing bowl. Increase the mixer speed to medium-high and add the vanilla extract and salt. Whip until the marshmallow is thick and slightly cool, 5 to 7 minutes. With a rubber spatula, scrape and spread the mixture into the pan. Let set at room temperature for at least 6 hours or overnight.
Once the marshmallow is set, coat the top with 1/2 cup remaining confectioners' sugar. Dust a cutting board with another 1/2 cup remaining confectioners' sugar. Release the marshmallow from the pan by running a knife around the sides, and then turn the marshmallow onto the cutting board. Cut into 1-inch strips with an oiled knife or a sharp pair of kitchen shears. Cut the strips into 1-inch cubes. Toss the marshmallows with the remaining 1 cup confectioners' sugar in a large bowl.
For the crust: Preheat the oven to 325 degrees F. Combine the graham cracker crumbs, butter, brown sugar, flour and salt in a medium bowl. Press into a 9-inch pie plate or 10-inch removable- bottom tart pan. Bake until the crust is just slightly browned, about 10 minutes. Do not overbake. Let cool while you make the filling.
For the filling: Increase the oven temperature to 350 degrees F. In a stand mixer fitted with the paddle attachment, beat the yams, brown sugar, butter, flour, salt, cinnamon, cloves, ginger and black pepper to combine. Add the eggs one at a time, beating until each egg is fully incorporated before adding the next one. Beat in the condensed milk until smooth. Pour the filling into the crust and bake minutes until the custard is barely set, about 20 minutes. Cool completely.
To assemble and serve the pie: Preheat the broiler. Arrange the marshmallows in an even layer on top of the pie. Broil the pie just to lightly toast the marshmallows, about 1 minute. Alternatively, you can toast the marshmallows using a kitchen torch. Serve immediately.