It's the last 3/4 of Kreutzer Etude 3 from 40 studies, transcribed onto piano, All I need to do now is add the first 3 bars on the beginning. I got that far in a day with it. Every bit as good as Czerny. A real challenge. It's the one Alex Laing recommended for violin.
How long can you keep going it's wonderful for that! Even if you just do it hands separately.