How to Make It
In a food processor, pulse together the flour, sugar and salt. Add the butter and lemon zest and pulse until the mixture resembles coarse meal. Add the milk and pulse just until combined. Transfer the dough to a lightly floured work surface and gently knead until smooth. Divide the dough in half and pat each half into a smooth disk. Wrap in plastic and refrigerate until chilled, about 1 hour.
Arrange eight 4 1/2-inch fluted tart pans with removable bottoms on a baking sheet. Divide 1 disk of dough into 4 equal pieces and roll each piece out to a 6 1/2-inch round. Fit each round into a tart pan, pressing it into the side and trim the overhang. Repeat with the remaining dough and tart pans. Refrigerate the tart shells for 30 minutes.
Preheat the oven to 375°. Line each tart shell with foil and fill with pie weights or dried beans. Bake for about 25 minutes, or until the edges are lightly golden. Remove the foil and weights and bake for about 7 minutes longer, or until the pastry bottoms are golden. Let cool.
In a double boiler or heatproof bowl set over a saucepan of simmering water, whisk the citrus juice together with the eggs and 1/2 cup of the sugar until blended. Cook, stirring constantly with a wooden spoon, until the custard is smooth and thick, 10 to 12 minutes; do not let it boil. Remove from the heat and stir in the butter.
Strain the custard into a bowl and stir in the citrus zests. Divide the custard among the tart shells and let cool completely. Cover with a sheet of wax paper and refrigerate overnight.
Remove the tarts from the pans and arrange the figs on top. In a small saucepan, cook the remaining 1/2 cup of sugar with the water over moderate heat, stirring occasionally, until the sugar is dissolved and the syrup is slightly thickened, about 5 minutes; let cool. Brush the syrup over the figs and serve.