Mix all the ingredients in a large bowl.
In a second bowl, combine all of the ingredients except for the vinegar. Carefully stir the liquid ingredients into the dry ingredients until a homogeneous consistency is achieved (don't stir too vigorously or for too long!) Stir in the vinegar.
Transfer the tart mixture to the prepared tin.
To bake (with topping)
Arrange the pears and hazelnuts on top of the tart mixture.
Bake for approx. 35 mins. in the centre of an oven preheated to 180°C.