For the pastry
75g gram flour
75g non-dairy margarine (eg Pure)
For the filling
3 large tomatoes
7 finger-long sprigs of rosemary
Oven 180C. Place the cornflour, gram flour, margarine and sugar in a food processor and blend until it forms crumbs. Add the water and knead everything together until it becomes a dough. Roll out to around 2mm thick and use to line a 20cm-diameter tart tin.
Remove the leaves from three of the rosemary sprigs and dice the onions into reasonably large pieces. In a heavy-bottomed saucepan, fry the onions and rosemary leaves in a couple of tablespoons of olive oil until the onions become pale brown and soft. Spoon into the pastry case.
Slice the tomatoes into thick slices (about 1cm thick) and arrange over the onions. Add the remaining rosemary in a decorative way, then drizzle olive oil over it all. Place in the oven for around 35 minutes until the top has become browned and the pastry is cooked.