Preheat your oven to 350°F (175°C) and line a muffin tray with paper liners.
In a large bowl, beat the eggs and sugar until light and fluffy.
Add the milk, sunflower oil, melted butter, yogurt, and vanilla sugar, mixing until well combined.
Gradually sift in the flour and salt, folding gently until the batter is smooth. Avoid overmixing.
Divide the batter evenly among the muffin cups, filling them about ¾ full.
Bake for 18-22 minutes, or until a toothpick inserted in the center comes out clean.
Let the muffins cool for a few minutes before transferring to a wire rack. Serve warm or at room temperature.