Preheat the oven to 350F. Generously spray a pie pan with oil and set aside.
Begin by blanching the hazelnuts. In a medium saucepan, bring 6 cups of water to a boil. Slowly add 3 tablespoons of baking powder and the hazelnuts. Boil for 3 minutes. Meanwhile prepare an ice bath. Once the hazelnuts are ready, pour them through a colander. Transfer the boiled hazelnuts to the ice bath and peel them by rubbing the nuts through your fingers. Place the peeled nuts on a kitchen towel and pat them dry. Toast the nuts at 350 degrees F for 15 minutes, until lightly brown and fragrant.
Next, make the crust. In a food processor, combine the hazelnut flour, maple syrup, and salt and process until well combined. The crust should hold together when pressed between your fingers. If it's still crumbly, add 1-2 teaspoons of water until it begins holding together. Transfer the crust into the prepared pie pan and spread evenly on the tops and sides. Place in the refrigerator.
In a double boiler, melt your chocolate. You can make a double boiler by placing a metal bowl over a pot of boiling water. Make sure the bottom of the bowl doesn't touch the water or your chocolate will burn. Once your chocolate is melted, pour it onto your prepared pie crust, creating a thin bottom. Return to the refrigerator to let the chocolate set up.
To make the filling, first make the vegan egg replacers. Combine 3 tablespoons of egg replacer with 6 tablespoons of water, stirring it together until all the powder has dissolved and the mixture is thick and creamy. Set aside.
In a small saucepot over medium heat, heat maple syrup, brown sugar, corn syrup, and salt. Bring to a boil and boil for one minute. Remove from heat and add bourbon and butter, stirring until the butter has completely melted. Whisk in the vegan eggs and vanilla extract until the eggs are completely incorporated into the custard.
Once the chocolate has hardened, add your toasted hazelnuts. They should nearly fill the top. Top with you maple custard and bake for 50 minutes. The filling will bubble up but it shouldn't overflow. Your pie is done when the filling is only slightly wobbly. Remove from the oven. Let it cool for 1 hour before transferring it to the refrigerator and letting it chill completely. Let the pie chill at least 4 hours in the refrigerator before slicing and serving.