Combine the melted butter, erythritol, vanilla extract, and egg in a mixing bowl and mix until smooth.
Add the almond flour, baking powder, and cinnamon. Mix until a smooth batter forms.
Fold in the blueberries gently to avoid crushing them.
Grease an oven safe ramekin with butter and pour in the batter. Add a few extra blueberries on top if desired.
Bake for 12–15 minutes until a toothpick inserted into the center comes out clean or with a few crumbs.
Serve warm or at room temperature.
Video
Notes
Microwave Option: You can also cook the muffin in the microwave. Pour the batter into a microwave-safe ramekin and microwave on high for about 90 seconds, or until set.