Heat oven to 325ºF/ 160ºC. In a food processor, combine all dry ingredients; process until finely ground, then drizzle in the melted butter until the crumbs are coated. Press mixture onto bottom and sides of a 10-inch tart pan or pie dish. Bake until set, 12 to 15 minutes. Set crust aside to cool.

In a small bowl, place bourbon, vanilla and 2 tablespoons water. Sprinkle gelatin powder over liquid; set aside to set for 10 minutes while you whip the eggs and make sugar syrup.

In the bowl of an electric mixer fitted with the whisk attachment, start beating eggs on medium-low speed until fluffy.

Make the sugar syrup while eggs are whisking. In a small saucepan over medium-high heat combine 3/4 cup sugar and 1/4 cup water. Cook, stirring occasionally, until temperature registers 245°F/120°C (firm-ball stage) on a candy thermometer, about 5 minutes. When the sugar’s ready, turn mixer to high speed and carefully drizzle sugar mixture into eggs in a thin stream (you can pour it into a mixing jug first for easy pouring); continue to beat until mixture increases in volume and is pale yellow, about 5 minutes.

When the egg mixture is nearly ready, you'll need to soften the gelatine. Heat the bowl carefully in the microwave, 10 seconds at a time, until it's liquid. (If you'd prefer, you can heat the gelatine over a pot of boiling water on the stovetop.) Turn mixer back to low; add gelatin mixture to egg mixture. Add pumpkin puree, the spices, salt, and sour cream; mix to combine. Pour filling into crust; refrigerate until set, 4 hours or overnight.

To serve, whisk heavy cream, confectioners' sugar, and vanilla in a medium bowl until stiff. Spread the whipped cream evenly over the top of the pie with a spatula). Dot with candied pecans. Serve chilled.