Preheat your oven to 180°C. Line a muffin tin with paper liners or lightly grease it. In a large mixing bowl, whisk together the flour, sugar, Dr. Oetker Baking Powder, Dr. Oetker Vanilla Sugar, and salt.

In a separate mixing bowl, beat the eggs. Add the milk and butter, mixing well until combined. Pour the wet ingredients into the dry ingredients and stir gently until just combined. Be careful not to over-mix to avoid tough muffins.

Fold the chopped rhubarb into the batter using a spatula, ensuring it's evenly distributed. Divide the batter evenly among the prepared muffin cups, filling each about two-thirds full.

Bake in the preheated oven for 25 minutes, or until a toothpick inserted into the center of a muffin comes out clean. Once baked, remove the muffins from the oven and allow them to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.