For the donuts, lightly grease a donut pan and preheat oven to 325F. In a large bowl, whisk together almond flour, erythritol, protein powder, cinnamon, baking powder and salt. Stir in melted butter, eggs, almond milk, stevia and vanilla extract until well combined. Fill donut pan holes approximately 2/3 full and bake 15 to 18 minutes, or until donuts are lightly browned and set. Let cool in pan 5 minutes, then flip out onto a wire rack to cool completely. Repeat with any remaining batter. For the glaze, melt butter in small skillet over medium heat. Cook until butter is browned and fragrant, about 4 minutes. Remove from heat. Place powdered erythritol in a medium bowl. Slowly whisk in browned butter until well combined. Mixture will be thick. Stir in 1 tbsp of cream at a time until a spreadable consistency is achieved. Stir in vanilla extract. Spread glaze on cooled donuts and let set, about 20 minutes.