Clean and wash the rhubarb. Take off 50 g and put aside. Cut the remaining rhubarb into thin slices.
Mix butter or margarine with sugar, lemon zest and salt until creamy. Separate eggs. Set the egg whites aside. Stir the egg yolks into the fat. Mix the flour - except for 1 tablespoon - with the nuts and baking powder. Stir alternately with the milk into the egg mixture. Turn the rhubarb slices in 1 tablespoon flour and fold into the dough. Line a muffin tin with two paper liners each and distribute the batter in it.
Bake the muffins in the preheated oven at 150 ° C for about 20 minutes. In the meantime, beat the egg whites until stiff, finally sprinkling in 100 g of powdered sugar. Take out the muffins and spread the egg whites on top. Bake for another 10 minutes.
Let the muffins cool on a wire rack. Cut the rhubarb that you have set aside into fine strips and decorate the muffins with them.