Preheat your oven to 350°F (175°C). This ensures that the muffins bake evenly.
Line your muffin tin with parchment paper or muffin liners to prevent sticking, or lightly grease with butter.
In a large mixing bowl, combine the plain yogurt, melted butter, eggs, and vanilla extract. Whisk until well blended.
In another bowl, mix together the almond flour, baking powder, and granulated sweetener. Make sure there are no lumps in the almond flour.
Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Be careful not to overmix.
Gently fold in the blueberries and raspberries, ensuring they are evenly distributed throughout the batter.
Spoon the batter into the prepared muffin tin, filling each cup about three-quarters full.
Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, remove the muffins from the oven and let them cool in the tin for a few minutes before transferring them to a wire rack to cool completely.