For the homemade granola bar, first toast the hazelnuts with the cereal and flax seeds in a pan without fat.
Put everything in a bowl and let it cool down. Grate the lemon and orange peel. Squeeze out the juice. Cut the banana into small pieces and grate the apple.
Mix the citrus zest, juice and fruit with the grain. Beat off the egg whites and stir into the mixture. Spread the mixture on a baking paper. Cover with a second paper and roll out 1.5 cm thick.
Pre-cut into small bars – but do not cut all the way through. Bake first at 160° for 20 minutes, then at 250° for another 8 minutes. Leave in the slightly open oven until the bars have cooled a bit. While lukewarm, cut the homemade granola bar into pieces.