Preheat oven to 325F and grease a 10x15 inch rimmed sheet pan very well.
In a large bowl, whisk together the almond flour, sweetener, coconut flour, protein powder, baking powder, and salt. Break up any clumps with the back of a fork.
In a medium saucepan over medium heat, combine the butter, water, and cocoa powder, stirring until melted. Bring to a boil and then remove from heat. Add to the bowl.
Add eggs, vanilla extract, cream and water and stir until well combined. Spread in prepared baking pan.
Bake 15 to 20 minutes, until cake is set and a tester inserted in the center comes out clean.
In another medium saucepan, combine butter, cocoa powder, cream, and water. Bring to a simmer, stirring until smooth. Stir in vanilla extract. Add powdered sweetener 1/2 a cup at a time, whisking vigorously to dissolve any clumps. Whisk in xanthan gum.
Pour over warm cake and sprinkle with pecans. Let cool until frosting is set, about 1 hour.
Serves 20 (or more!). Each serving has 2.8 g NET CARBS. Sugar Alcohols (erythritol): 26.25g