650 gmmixed baby tomatoes, such as yellow grape, cherry and baby Roma½baby fennel bulb, shaved on a mandolin, plus fronds, to serve1salad onion, thinly sliced1½ cups(loosely packed) watercress sprigsTo serve:shaved parmesanParmesan pastry200 gm (1 1/3 cups)plain flour150 gmchilled butter, coarsely chopped50 gmfinely grated parmesanMustard dressing1 tbspolive oilJuiceof 1 lemon½ tspDijon mustard
For parmesan pastry, process flour and butter in a food processor until fine crumbs form. Add parmesan, process to combine, add 40-60ml iced water, pulsing to form a dough. Turn onto a lightly floured surface, knead lightly to form a disc, wrap in plastic wrap and refrigerate until chilled (1 hour). Roll out on a lightly floured surface to a 35cm-diameter round and line a 25cm-diameter tart tin, trim edges and prick base with a fork. Refrigerate to rest (30 minutes).
Meanwhile, preheat oven to 180C. Blind bake pastry until light golden (15-25 minutes), then remove paper and weights and bake until golden and crisp (5-10 minutes). Set aside to cool.
For mustard dressing, whisk ingredients in a large bowl to combine, season to taste and set aside.
Add tomato, fennel, spring onion and watercress sprigs to dressing, toss lightly to combine, season to taste, then transfer to pastry case. Scatter over parmesan and fennel fronds and serve immediately.