1. Preheat oven to 350°F (175°C). Lightly grease a small baking dish (about 8×8 inches).

2. In a medium bowl, whisk together almond flour, coconut flour, baking powder, and salt.

3. In a large bowl, beat egg yolks with sweetener until pale and creamy.

4. Add lemon zest, lemon juice, milk, melted coconut oil or butter, and vanilla extract to the yolk mixture and whisk well.

5. Gradually stir the dry ingredients into the wet mixture until smooth.

6. In a separate bowl, beat egg whites until soft peaks form.

7. Gently fold the egg whites into the batter in two batches.

8. Pour batter into the prepared dish and evenly scatter blueberries over the top.

9. Place the dish inside a larger baking pan and pour hot water into the outer pan halfway up the sides.

10. Bake for 30–35 minutes, or until the top is golden and set, but a slight jiggle remains underneath.

11. Carefully remove from oven and water bath. Let cool slightly before serving.