First, bake the sweet potatoes unless you are able to find canned sweet potatoes (for some reason, I never have much luck finding canned). Set out the mascarpone cheese so it can soften while you bake the potatoes.
Once you’ve poured the filling into the crust, bake at 350°F for 48-50 minutes, until the center is set but the pie may still have a slightly jiggle to it if you were to shake it. A little jiggle is OK, but you don’t want the pie to look like liquid (like it did before baking). Allow to cool before serving or storing.
Spray a 8×8 pan with non-stick cooking spray and lightly dust with half of the powdered sugar (2 tablespoons). Set the rest aside.
Set up your stand mixer with a whisk attachment. Pour 1/2 of the water and the gelatin into the bowl and allow that to sit for 10 minutes (don’t mix it). In the meantime, in a pot over high heat stir together the remaining 1/4 cup water, the sugar, the corn syrup, and salt. Attach your candy thermometer and allow mixture to reach 240 F. Remove from heat. Start your mixture on low and pour the hot sugar water into the mixer as it is running. Be careful! I always use my splash guard for this step. Once you’ve poured in all the sugar water, turn the mixer on high and beat until white and fluffy (7-10 minutes). You can add the bourbon and vanilla extract to the mixer as it’s running during the first few minutes. Then pour the marshmallow batter into your prepared dish, sprinkle with the remaining powdered sugar, cover and allow to set overnight.
Go around the edge of the pan with a knife and plop the marshmallows out onto a cutting board. Cut with a pizza cutter or kitchen shears. You can store these in an airtight container or plastic bag. Once you are ready to serve your pie, top with the marshmallows and toast with a kitchen torch or for a few minutes under your kitchen broiler, just until the marshmallows look nice and toasty.
If you want to use store-bought marshmallows to top this pie with instead, feel free.