Preheat oven to 350°F (175°C). Grease a 6-cavity donut baking pan with 1 teaspoon of the melted butter.
Make the donuts: In a large bowl, stir together the almond flour, coconut flour, erythritol, baking powder, nutmeg, and 1/4 teaspoon sea salt.
In a small bowl, whisk together the remaining 6 teaspoons melted butter, cream, eggs, and 1/2 teaspoon vanilla extract.
Whisk the wet mixture into the dry mixture until smooth, then evenly divide the batter into the donut cavities, filling them 3/4 of the way (if you have extra batter, discard it; do not overfill). Bake until dark golden brown, 18 to 20 minutes, rotating the pan halfway through cooking. Remove and cool on a wire rack for 5 minutes.
Set a wire rack over a baking sheet. When the donuts are cool enough to easily remove from the molds, transfer them to the wire rack to continue cooling.
Make the chocolate glaze: Melt the unsweetened chocolate and the coconut oil in a medium glass or metal bowl set over simmering water. Whisk in the powdered sweetener and cocoa powder, then whisk in the remaining 1/2 teaspoon vanilla extract and 2 tablespoons water. If the glaze is too thick to be pourable, thin it with a little bit of water.
Working one at a time, dip the rounded top side of a donut into the chocolate glaze, then return it to the wire rack. Repeat with the remaining donuts, whisking the glaze between dips. Immediately top the donuts with the unsweetened coconut. Serve.