Preheat the oven to 375℉ and line a large baking sheet with parchment paper.
Using an electric mixer with a paddle attachment, combine Keto Chow, psyllium husk powder, coconut flour, erythritol, baking powder, orange and lemon zest, cinnamon, allspice, and nutmeg. Mix on low to combine.
Add the melted butter and boiling hot water. Carefully mix on the lowest setting until the water is absorbed, then turn the speed up to medium and mix until a soft dough forms.
Add the dried blueberries, if using, and mix briefly to incorporate them into the dough.
Divide the dough into eight equal pieces and roll them into balls. Wet your hands lightly with cool water if they are too sticky to roll. Space them evenly on the prepared baking sheet.
Bake for 30-40 minutes, or until golden brown, round, and puffed. They should sound slightly hollow when tapped on the bottom.
Serve warm with plenty of butter or allow them to cool completely and decorate with royal icing.
To make the icing, stir heavy cream and lemon juice into the powdered erythritol. If it is too thick, add more heavy cream or water a tsp. at a time until thin enough to pipe but still thick enough to hold together in a string when piped.
Pipe a cross or other decorative shapes on the cooled buns and allow the icing to set for at least half an hour before serving.