Whisk the egg, egg yolk, milk and cream together and mix with the flour until smooth. Season with salt and pepper. Bake 6 golden-brown crepes one after the other in a lightly oiled pan and let them cool.
Roughly chop the watercress. Clean the radishes and cut into thin slices. Mix both in the quark and season with salt and pepper.
Brush the crepes with the watercress quark and roll them up.