Preheat your oven to 180°C (350°F) and prepare a large baking sheet with parchment paper.
In a large mixing bowl, combine coconut flour, almond flour, 3 tablespoons of sweetener, and baking powder.
In a separate bowl, whisk together heavy cream, coconut oil, one whole egg, one egg yolk, and vanilla extract until smooth.
Gently fold the wet ingredients into the dry, then fold in the blueberries. Knead until mostly smooth.
Dust a flat surface with almond flour, transfer the dough, and knead into a ball. Flatten into a thick disk and cut into 8-10 triangles.
Arrange scones on the baking sheet, brush with egg white, and sprinkle with remaining sweetener.
Bake for 20-25 minutes until golden. Allow to cool completely before serving.