Preheat oven to 350°F (175°C). Whisk almond flour, coconut flour, erythritol, and ¼ tsp salt. Cut in 6 tbsp butter until crumbly, then stir in 1 egg to form a dough. Press into a 9-inch pie pan and prick with a fork.

Line crust with parchment and weights, bake 10 minutes, then remove weights and bake 5 minutes more until edges are pale gold.

Toast pecans in a dry skillet 3 minutes until fragrant. Melt remaining ½ cup butter in a saucepan over medium heat and cook until golden, about 3 minutes. Remove from heat, whisk in sweetener and vanilla, then whisk in 3 eggs one by one, followed by cream and remaining ¼ tsp salt. Fold in toasted pecans.

Pour filling into prebaked crust. Reduce oven to 325°F (160°C) and bake 35 to 40 minutes until edges are set and center barely jiggles. Cool on a rack at least 2 hours.

Once cool, run a knife around the edge, slice into 8 wedges, and serve.