Preheat your oven to 375°F (190°C).
In a large bowl, whisk together the almond flour, coconut flour, protein powder, sweetener, baking powder, and salt until everything is well combined.
Stir in the sour cream, eggs, and vanilla extract. Mix well until a soft dough forms. If it feels too wet, you can add an extra tablespoon of coconut flour.
Gently fold in most of the fresh blueberries, saving a few to sprinkle on top later. Let the dough rest for 5 minutes.
While the dough rests, place 1 tablespoon of butter in a 10-inch oven-safe skillet (cast iron works wonderfully). Put the skillet in the preheated oven for a few minutes to melt the butter.
Carefully remove the hot skillet from the oven. Lightly flour your hands (with coconut flour) and shape the dough into about 10 small, 2-inch balls. Arrange these balls in the hot skillet. Press the remaining blueberries onto the tops of the biscuits.
Melt the remaining 1 tablespoon of butter and drizzle it over the formed biscuits. Return the skillet to the oven and bake for 20 to 25 minutes, or until the biscuits are golden brown and firm to the touch.
Take the skillet out of the oven and let the biscuits cool for at least 20 minutes. For the glaze, whisk together the powdered sweetener and lemon juice. Drizzle this glaze over the cooled biscuits right before serving.