Cook parsnip and cauliflower separately until soft. Puree in food processor until smooth. Transfer mixture to bowl and mix in vinegar and a tablespoon of the olive oil. Season with a couple of pinches of salt.
Heat half the remaining olive oil in a pot over a medium heat and add flour,whisking and toasting it for a minute.
Add milk and parmesan,and whisk well for 30 seconds so no lumps form.
Remove saucepan from heat and add egg yolks,whisking well to incorporate them.
Add this flour-egg mixture to the puree,add 200 grams of the mozzarella dice (keep rest for final plating) and mix well. Check for salt and add a little white pepper.
Whisk egg whites to soft peaks and fold into the mixture.
Oil eight individual ceramic bowls or one large baking-flan dish with remaining olive oil and line with breadcrumbs.
Pour mixture in and bake in an oven preheated to 200C. It should take 15 minutes for individual bowls or 25 to 30 minutes for a large dish.
Remove from oven and cool a little before turning out and serving with treviso or other lettuce and remaining mozzarella dice.