Preheat oven to 425 degrees F.

Using your food processor, combine flour, butter, sugar, salt and zest. Pulse the mixture until it resembles a coarse meal with some small lumps that are about the size of a pea mixed in. Add the egg yolks and process until the mixture begins to come together in a clump.

Place the dough mixture onto your work surface and divide it into 2 portions. Smear each portion once with the heel of your hand (using a forward motion). This will help distribute the fat in the dough. Put the two portions together and form into a ball.

Put the ball of dough into a tart pan. With floured fingers, press the dough into the tart pan. You want an even 1/4 inch layer of dough covering the bottom of the pan and extending up the sides of the pan. (Use a tart pan with a removable bottom) Chill the dough in the tart pan for approximately 30 minutes--until it is firm.

To prepare the filling for the tart, mix the sugar and cornstarch together in a large bowl. Next, add the plums and the lemon juice and toss the mixture to coat the plums. Let this mixture stand for approximately 30 minutes. Stir the mixture occasionally. You want to have a juicy mixture of plums to arrange in your tart shell.

Arrange the plum slices in the tart shell in concentric circles. Pour the juices in the bowl over the plums in the tart. (I had some juice left over the last time I made this tart. I was using particularly juicy plums. I didn't want to fill the tart shell to overflowing and did not use all the liquid.)

Bake your tart in the middle of your oven for 15 minutes at 425 degrees F. After 15 minutes, take the tart out of the oven and loosely cover it with foil. Return to the oven and bake the tart for 40 to 50 minutes at 375 degrees F. When the tart is properly baked, the plums will be tender and the juices will be bubbling and slightly thickened.

Cool tart completely before trying to remove it from your tart pan.