1.Make parmesan pastry. Process flour, butter and parmesan until crumbly. Add egg yolk and enough of the water to make ingredients come together. Turn dough onto a floured surface; knead gently until smooth. Wrap pastry in plastic; refrigerate 30 minutes.
2.Oil a 12.5cm x 35cm (5-inch x 14-inch) rectangular loose-based tart tin. Roll pastry between sheets of baking paper until large enough to line tin. Ease pastry into tin, press into base and sides; trim edges. Place on an oven tray; refrigerate 30 minutes.
3.Preheat oven to 180°C/375°F.
4.Line pastry case with baking paper, fill with dried beans or rice. Bake 15 minutes. Remove paper and beans; bake a further 15 minutes. Increase oven to 200°C/400°F.
5.Meanwhile, melt butter in a medium frying pan; cook asparagus over medium heat, stirring, 5 minutes or until tender. Remove from pan. Whisk eggs, cream and herbs together in a large jug. Arrange asparagus in rows in pastry case, allowing the ends to stick out over the rim. Pour egg mixture over asparagus; sprinkle with gruyère.
6.Bake tart 30 minutes or until filling is just set. Stand 10 minutes.
7.Meanwhile, make asparagus salad. Using a wide vegetable peeler or mandoline, peel green and white asparagus into long thin ribbons. Tear prosciutto slices into thirds. Place asparagus and prosciutto in a bowl with parmesan and feta; toss gently to combine.
8.Serve tart topped with asparagus salad.