Using a food processor fitted with a coarse grating disk, grate the potato and onion; discard any large pieces. Transfer the mixture to a clean dish towel and squeeze out any excess liquid then transfer to a large bowl. Stir in the flour, egg, 3/4 teaspoon salt, 1/4 teaspoon pepper and the baking powder.
In small bowl, whisk together crème fraîche, horseradish and a generous pinch of salt; cover and refrigerate.
To a food processor, add beets then combine with potatoes and onions. Add scallion greens and dill to batter.