It's hard to believe that two oranges and one lemon add up to eight servings of outrageous citrus flavor, but in this tart, they do. The zest (that is the colorful outermost rind) of the lemon goes into the crust. The juices and the zest of one of the are transformed into a smooth and sumptuous custard to make the filling. Serve this tart with a compote of strawberries and oranges (p. x) after a formal dinner or serve it unadulterated with cups of espresso as an afternoon pick-me-up. Use a microplane grater to get the zest off the citrus fruits.

For the crust:

1 cup unbleached white flour

1/2 cup cold unsalted butter, cut into 1-inch bits

2 tablespoons sugar

1/2 teaspoon table salt

1 egg white

1 teaspoon freshly grated lemon zest

For the Filling:

3 eggs

1 egg yolk

1 cup sugar

1 tablespoon orange zest

3/4 cup freshly squeezed orange juice (from 2 medium oranges)

1/4 cup freshly squeezed lemon juice (from one medium lemon)

1.) Preheat the oven to 375 and line the bottom of a two-piece 10-inch spring form pan with a circle of baker's parchment or spray it with non-stick spray.

2.) To make the pastry for the crust, put the flour in the work bowl of a food processor, or in a mixing bowl. Work in the butter, sugar and salt. If using a food processor, process just until mixture resembles coarse crumbs; leave some chunks of butter about the size of bee-bees. Add the egg white and pulse the motor or work the mixture with a wooden spoon just until the dough comes together into a scrappy heap. Do not knead or overwork; it is not necessary to make the dough into a smooth ball.

3.) On a floured surface, roll the pastry dough into a 10-inch circle and plant the circle in a pie pan. Line the pastry with a piece of baker's parchment or aluminum foil and fill it with rice or beans or special pie weights. Bake the pastry until the edges are lightly browned, about 20 minutes. Remove the parchment with the rice or beans and bake until the center of the crust is dry and just beginning to turn golden, about 5 minutes more.

4.) While the crust is baking, whisk together the eggs with the egg yolk, and sugar. Then whisk in the orange zest, orange juice and lemon juice. When the crust is baked, pour in the filling, put the tart back in the oven and bake until the filling is barely set, with a slight jiggle in the center, about 25 minutes.

5.) Cool the tart completely before attempting to unmold it, about 1 hour. Serve at room temperature or refrigerate and serve chilled.