Preheat and prep: Heat your oven to 350°F (175°C). Lightly grease a 6-cavity nonstick donut pan.
If yours is silicone, place it on a baking sheet for stability.
Mix dry ingredients: In a medium bowl, whisk almond flour, coconut flour, sweetener, baking powder, baking soda, salt, and cinnamon. Break up any lumps for an even batter.
Whisk wet ingredients: In a separate bowl, whisk eggs, sour cream, almond milk, vanilla, and melted butter until smooth. The mixture should be glossy and uniform.
Combine: Add dry ingredients to wet and stir with a spatula until just combined.
The batter will be thick but scoopable. Avoid overmixing to keep the crumb tender.
Fill the pan: Spoon or pipe the batter into the donut cavities, filling each about 3/4 full. A zip-top bag with the corner snipped makes neat work.
Bake: Bake for 14–17 minutes, until the donuts are set and lightly golden at the edges.
A toothpick should come out clean or with a few moist crumbs.
Cool: Let them cool in the pan for 5 minutes, then gently remove and place on a wire rack. This helps them firm up and prevents breakage.
Glaze (optional): Whisk powdered sweetener, cream or almond milk, vanilla, and a pinch of salt until smooth. Dip the cooled donuts or drizzle over the top.
Let the glaze set for 10–15 minutes.
Serve: Enjoy as is, dust with extra powdered sweetener, or finish with a sprinkle of cinnamon.