The quantities are set according to how much you want to get out. I used 2 large potatoes, half a larger celery root, 1 large beetroot.
we proceed like this: we clean the beets, we cut it into bigger cubes, we put salt, pepper and in a tray covered with aluminum foil in the oven for about 50 minutes, they are ready when the toothpick test passes. then prepare the celery: clean it and cut larger cubes, season with salt and pepper and bake for about 40 minutes. at the end we do the same with the potatoes, cleaned, cut into cubes similar to the other vegetables, season with salt and pepper and bake for about 30 minutes.
meanwhile we make mayonnaise from a raw yolk, 1 teaspoon mustard a little salt and gradually we put oil in a thin thread, we put lemon juice and let it cool. when the vegetables are ready cooked and cooled, mix them and make the dressing as follows: mix the sour cream with mayonnaise, the mustard spoon and the horseradish spoon and put it over the vegetables. if necessary, add salt, pepper and lemon juice and let it cool until ready to serve.