Rub flour, butter, icing sugar, and salt together until the mixture resembles fine breadcrumbs.
Mix in the egg to form a dough and knead lightly until smooth.
Flatten the dough into a ball, wrap in cling film, and chill for 30 minutes.
Preheat the oven to 170°C and grease a 25cm tart ring.
Whisk eggs, sugar, cream, lemon zest, and juice together, then chill the mixture.
Roll the pastry on a floured surface to a 3mm thickness.
Line the tart ring with pastry on a baking sheet, leaving excess over the edges.
Fill the pastry with weights using cling film or parchment and bake for 15 minutes.
Remove weights, brush with beaten egg, and bake for 4 minutes until golden.
Reduce the oven temperature to 150°C.
Skim any bubbles off the surface of the chilled lemon cream.
Pour half the filling into the case, move to the oven, and add the remaining filling.
Bake for 60 minutes until set with a slight wobble, then cool at room temperature.
Dust with sugar, glaze with a torch or grill, and serve with crème fraîche.