Whisk the egg yolk and sugar. Add mayonnaise and beat a little again. Add flour, baking powder and knead to a soft dough.
Wash the rhubarb, pat dry and remove the top layer.
Roll out the dough into a 5 mm thick layer. Place the rhubarb on the edge and wrap the dough in one turn. Cut off the excess dough, pinch the edges, roll a little on the table.
Cut into pieces about 5-6 cm long. Beat the protein with a fork, dip the pieces into the protein.