Preheat oven to 350 degrees F. In a mixing bowl combine almond flour, baking soda, salt, and spices. Mix butter, sweetener, eggs and pumpkin until smooth. Stir wet ingredients into dry. Grease and pour into a pumpkin cake pan. Bake 60-70 minutes, or until a toothpick inserted in the middle comes out clean (you may want to loosely cover with tinfoil so the outside doesn't brown too much). Decorate with brown butter frosting.
To make the Filling: place the butter in a saucepan and heat on high until the butter sizzles and you can see lots of brown (not black) flecks.
Remove from heat and add the mascarpone or cream cheese, almond milk and natural sweetener.
Stir until very smooth. Set aside to cool. This will thicken overnight. Use to decorate cake.