Preheat the oven 350 degrees F. Spray a 9" removable bottom tart pan with nonstick cooking spray. 

Melt the butter in a pan over medium heat, whisking until it foams, then eventually browns. This should take about 4-5 minutes. Pour the browned butter in a heat-proof bowl and set aside.

In a food processor, crush the gingersnaps until finely ground. Pour in the melted brown butter, and pulse until thoroughly incorporated. Pour the crumbs into the prepared tart pan. Use the bottom of a drinking glass or a measuring cup to really press down the crumbs evenly into pan, and up the sides. Place the crust on a rimmed baking sheet, and bake for 15 minutes. Remove the pan from the oven, and set aside. 

In a medium size mixing bowl, combine the sugar and the ground spices, whisk to combine. Add the egg, heavy cream, and sour cream together, and whisk thoroughly. Add the canned pumpkin, vanilla extract and salt, and whisk well until smooth. Pour the pumpkin custard into the crust, and return to the oven for 45-50 minutes, until the custard is set, and not at all soupy. Cool at room temperature for an hour, then refrigerate for at least two hours. Remove the tart from the refrigerator at least 45 minutes prior to serving. Top the tart with soft whipped cream and roasted pumpkin seeds.