Combine quark, milk, oil, 75g sugar, vanilla sugar, flour, and baking powder in a mixer with dough hook or in a food processor. Mix for 2-3 minutes until you have a firm dough that doesn't stick to the sides.
Roll out the dough into a rectangle on parchment paper. Grate the apples and spread them evenly over the dough. If the grated apples release excess liquid, gently squeeze the mixture with your hands to remove it.
Using the parchment paper to help, roll the dough tightly into a log. Cut the log into slices about 1-2 cm thick and place them on parchment paper, spacing them slightly apart.
If desired, sprinkle finely chopped nuts over the snails, or mix them with the grated apples before spreading on the dough.
Bake in a moderate oven at 160°C (320°F) for 30-40 minutes until light golden.
While the snails bake, prepare a glaze. When the snails come out of the oven and are still warm, brush or drizzle the glaze over them.