Preheat oven and line pan:
Heat oven to 350°F (180°C, 160°C convection). Place paper liners in a muffin pan.Peel, core, and dice apples:
Remove apple skins, take out cores, and dice into small chunks.Beat quark, eggs, and oil:
In a large bowl, beat quark, eggs, and sunflower oil until uniform.Mix dry ingredients into batter:
Mix in sugar, flour, baking powder, cinnamon, and salt; blend until a smooth batter forms.Fold in apple chunks:
Carefully incorporate apple chunks into the batter, ensuring even distribution.Fill muffin cups:
Portion batter equally into the muffin cups, filling each roughly three-quarters full.Bake until golden and clean:
Bake in the preheated oven for 20-25 minutes, until tops are golden and a toothpick inserted in the center emerges clean.Cool in pan then on rack:
Allow muffins to rest in the pan for a few minutes, then move them to a wire rack to cool fully.Dust with powdered sugar:
Optionally, sprinkle with powdered sugar before serving.