1
Whisk eggs, yolk, sugar and lemon juice until well combined; whisk in double cream. Stir through rosemary and zest. Cover and refrigerate overnight for flavours to infuse.
2
Meanwhile, for rosemary pastry, process flour, icing sugar and a pinch of salt in a food processor; add butter and process until coarse crumbs form. Add egg, rosemary, zest and 2-4 tsp iced water and pulse until just combined. Lightly knead, then form into a disc, enclose in plastic wrap, and refrigerate for 1 hour (see note).
3
Remove pastry from fridge and set aside for 20 minutes. Roll out pastry on a lightly floured piece of baking paper to a 3mm-thick 6cm x 40cm rectangle, then line a greased 10.5cm x 34.5cm rectangular loose-based tart tin, trimming excess pastry. Reserve trimmed pastry, enclose in plastic wrap and refrigerate. Lightly prick base of tart shell with a fork; refrigerate for 1 hour.
4
Preheat oven to 180°C. Place tart shell on an oven tray. Line pastry with a large piece of foil and fill with pastry weights or rice. Blind-bake tart shell until edges are pale golden and side is set (30 minutes). Reduce oven to 170°C. Remove foil and weights, then bake until light golden and crisp (8-10 minutes). Repair any cracks or holes with reserved pastry. Brush with egg-yolk mixture and cook until crisp (5 minutes). Remove from oven.
5
Reduce oven to 150˚C. Remove lemon filling from fridge. Skim any foam that has formed on top, then strain filling through a fine sieve. Carefully pour half the filling into tart shell. Place in oven, then fill to the rim. Bake until set around edges but centre still has a slight wobble (20-25 minutes). Cool tart in tin for 2 hours, then remove from tin and cool completely (if you leave tart in tin for too long the pastry will sweat).
6
Whisk crème fraîche and icing sugar to soft peaks. Carefully slice tart and serve with crème fraîche and rosemary flowers. Tart is best eaten on day it’s made.
