Combine the almond flour, coconut flour, sweetener, salt, and coconut oil until mixture resembles coarse meal.
Press the flour mixture into a 13 x 9-inch baking dish coated with cooking spray.
Bake at 350° for 15 minutes, or until crust is golden brown.
Combine eggs, sweetener, milk, cream, and vanilla, then add xantham gum and rhubarb.
Pour the egg mixture over the partially baked crust and return to oven.
Bake for 50 minutes, or until custard has set, then remove from the oven and cool.
Combine cream cheese, sweetener, and vanilla, then spread over top.