Preheat the oven to 325 degrees. Fill a medium saucepan one-third full with water and bring to a simmer. Put the zest and lemon juice in a medium bowl and whisk in the eggs. Add the sugar and butter and place the bowl over the simmering water; the water must not touch the bottom of the bowl. Cook, whisking constantly, until the butter is completely melted and the mixture is smooth. Remove the bowl from the pan of hot water and allow the mixture to cool for 15 minutes. Place the pre - baked tart shell on a baking sheet. Pour the filling into the shell and bake the tart for 8 to 10 minutes, or until the center is just set. Cool the tart completely on a wire rack. Make the garnish: Using a channel knife, cut 6 lengthwise grooves in the lemon, removing 6 strips of rind. Cut a crosswise slice from the center of the lemon and place it in the center of the tart. Slice the remaining lemon and place it in the center of the sections into half and then cut the sections into halfmoons. Arrange the slices around the edge of the tart with the cut sides out. If necessary, rewarm the apricot glaze over low heat or in the microwave. Using a pastry brush, lightly brush the top of the tart with the warm apricot glaze. Garnish with a few mint leaves.
Sift together the confectioners' sugar, flour, and salt into a bowl. Place the butter in a food processor and process until smooth, about 15 seconds. Scatter the flour mixture over the butter, add the egg, and process just until the dough forms a mass; do not overmix. Turn the dough out onto the counter and divide it into 2 pieces. Shape each half into a disc, wrap in plastic wrap, and refrigerate.