From which pianist's biography?

[lemppari]

Hi,

I remember reading some very famous pianist's biography many years ago. He told that when he was young, he had a new teacher (in Paris?) who made him play and practice just one note for a long time.

For some reason this anecdote came to my mind recently and I wanted to check who that pianist was. First I was sure it was Arthur Rubinstein, but I have his book "My Young Years" and I don't find this story there. Can you help me, where this story came to my head?

Cheers,
Kari