For crème fraîche pastry, process flour, butter and 1 tsp sea salt in a food processor until fine crumbs form, add crème fraîche and process until pastry just comes together. Form into a disc, wrap in plastic wrap and refrigerate to rest (1 hour).
Preheat oven to 180C. Roll out pastry on a floured surface to 3mm thick, line a 24cm-diameter tart tin, trim edges and refrigerate to rest (30 minutes). Prick base and blind bake until light golden (10-12 minutes). Remove paper and weights, bake until crisp (6-8 minutes), brush with eggwash, bake until glazed (2 minutes) and set aside.
Blanch peas until just tender (4-5 minutes), drain and set aside. Heat butter in a large frying pan over medium-high heat, add spring onion and garlic, stir occasionally until tender (4-5 minutes), add cos, stir until wilted, season to taste and set aside.
Whisk yolks, crème fraîche and lemon rind in a bowl to combine and season to taste. Stir in peas, herbs and and lettuce mixture. Spoon into pastry case, spreading evenly, scatter with Gruyère, bake until golden and just set (15-20 minutes) and stand to cool for 15 minutes.
For salad, blanch peas until just tender (4-5 minutes), remove with a slotted spoon, refresh and drain. Blanch sugarsnap peas until just tender (2-3 minutes), drain, refresh and drain. Combine in a bowl with tendrils and cos. Whisk lemon juice, mustard and crème fraîche in a small bowl, whisk in oil and season to taste. Pour over pea mixture, toss to coat and serve with warm tart.
This recipe is from the October 2012 issue of Australian Gourmet Traveller.