Preheat the oven to 325F and grease an 8x8 inch metal baking pan.
In a large bowl, whisk together the almond flour, sweetener, coconut flour, and salt. Stir in the butter and vanilla extract and toss until mixture resembles coarse crumbs.
Press 2/3 of the mixture firmly into bottom prepared baking pan. Bake 8 minutes, until just golden on the edges and then remove (it will not be baked through).
In a large saucepan, heat the whipping cream and powdered sweetener over medium heat, stirring to combine. Bring to barely a simmer and remove from heat. Add the chopped chocolate and let sit 5 minutes to melt.
Whisk filling until smooth, then add the vanilla. Sprinkle with glucomannan and whisk to combine. Pour the filling over the crust and spread to the edges.
Sprinkle the surface with the remaining crumb mixture. Bake 22 to 25 minutes, until topping is golden brown. Remove and let cool completely.