Preheat oven to 425°F (220°C). Place an 8- or 9-inch cast-iron skillet inside to heat while you prepare the batter.
In a medium bowl, whisk together almond flour, yogurt, eggs, butter, vanilla, baking powder, salt, and sweetener until smooth and pourable.
Fold in blueberries.
Carefully remove the hot skillet, grease lightly with butter or oil, and pour in the batter.
Bake 14–16 minutes until puffed and golden around the edges.
Cool slightly — the center will gently fall as it settles — then sprinkle with date sugar or your preferred topping.