Whiz the flour, icing sugar and butter in a food processor until the mixture resembles coarse breadcrumbs. Add 1 egg and whiz until mixture comes together (you may need to add a little iced water if the pastry is not coming together). Form pastry dough into a ball and wrap to refrigerate for 30 minutes.
Preheat over to 190°C and grease a 24cm loose-bottom tart pan with margarine or butter. Line the tart pan with baking paper and fill with pastry weights before baking for 10 minutes.
Roll out pastry on a floured surface until 4mm thick, then quickly lay out over tart base with pastry weights. Trim the excess and chill for another 30 minutes.
Reduce the oven to 150°C. Beat the mascarpone, caster sugar, 3 eggs and 4 egg yolks with an electric beater until just combined, then beat in the lemon zest and juice. Pour into tart shell and tart pan and bake for 50-55 minutes, or until set. Cool slightly.