1) Prepare pastry dough. In small bowl, with mixer at medium speed, beat lemon peel, butter and sugar until well blended; beat in egg yolk. Stir in cake flour until just blended. Shape dough into a ball; wrap in plastic wrap and refrigerate for 1 hour.
2) Preheat oven to 425º F. On lightly floured surface, with floured rolling pin, roll out dough into a round about 1 inch larger all around than your removable bottom tart pan. Ease dough into tart pan to line evenly; trim edge even with the rim. With fork, prick tart shell in many places to prevent puffing and shrinkage during baking. Line tart shell with foil.
3) Bake tart shell 10 minutes; remove foil and again prick the shell. Bake 5 minutes longer or until pastry is golden. (If pastry puffs up, gently press it back with a spoon) Cool tart shell on a wire rack.
4) Prepare filling: In heavy 2 quart saucepan, with wire whisk or fork, beat eggs and yolks until blended; stir in lemon juice and 1 cup sugar. Cook over medium low heat, stirring constantly until mixture thickens and coats a spoon well, about 15 minutes (mixture should be about 170º to 175º, but do not boil or it will curdle) Stir in the butter until melted.
5) Into baked tart shell, pour lemon custard filling.
6) Refrigerate tart overnight so that filling is well chilled and firm.
7) About 1 to 2 hours before serving, preheat broiler. Cover edge of crust with foil to prevent over browning. Evenly sprinkle the remaining 3 Tb of sugar over the lemon custard filling.
8) Place tart in broiler at closest position; broil 6 to 8 minutes until the sugar melts and begins to brown, making a shiny crust. Chill
9) Carefully remove side of tart pan; slide tart onto a cake plate. In small saucepan over low heat, melt the apricot preserves. Brush top of tart with melted preserves.
To serve garnish the center of the tart with lemon slices.