The day before mix olive oil and grape seed oil, add grated truffles, salt and leave overnight. Peel and wash the turnips, cut into slices and cook until soft. Puree with olive oil, season and pass through a sieve. Pour into small bowls and refrigerate. Bring vegetable stock to a boil with the cornflour, add salt, boil for 3 minutes and also chill. Before serving, add vegetable stock to truffle mixture, whisk vigorously and strain. Spread over the beet puree and refrigerate.