Preheat your oven to 350°F (175°C). Grease a standard 6-cavity donut pan well with butter or cooking spray.
In a medium bowl, whisk together the almond flour, cocoa powder, erythritol, baking powder, and salt.
In a separate bowl, whisk the eggs, melted butter, sour cream, and vanilla extract until smooth. Add the wet ingredients to the dry ingredients and stir until a thick, uniform batter forms.
Spoon or pipe the batter into the donut cavities, filling each about three-quarters full. Smooth the tops gently with the back of a spoon.
Bake for 18 to 22 minutes, until the donuts spring back when lightly touched. Let them cool in the pan for 5 minutes, then turn them out onto a wire rack to cool completely.
Make the glaze by melting the chopped sugar-free dark chocolate and coconut oil together in a small microwave-safe bowl in 20-second intervals, stirring between each. Stir in the powdered erythritol until smooth.
Dip the top of each cooled donut into the chocolate glaze, let any excess drip off, then set them back on the wire rack. Let the glaze set for about 15 minutes before serving.