To Make the Dough:

Place the flour, salt, and sugar in the bowl of a food processor fit with a metal blade and pulse to combine.

Add the buttery sticks and pulse until the mixture resembles a coarse meal. (There should be pieces of margarine the size of peas and some slightly large pieces as well). Add the egg yolks and process until the egg yolks are combined and the dough just starts to come together.

Transfer the dough to a bowl. If you can press it into a smooth ball do not add any water. If the dough is still crumbly add the water 1tablespoon at a time until it you can press it into a smooth ball.

Divide the dough into two pieces, with 2/3 of the dough and the other with 1/3. Place each piece of dough on a piece of plastic wrap and flatten the dough into a rectangle one inch thick. Wrap well and refrigerate for one hour. (If you are in a real hurry you can freeze it for 15 minutes.) The dough can be kept refrigerated for up to five days or frozen, well wrapped, for up to a month.

To Make the Pie:

Preheat the oven to 375.

Remove the larger piece of dough from the refrigerator and transfer it to a lightly floured piece of parchment paper. Top with an additional sheet of parchment and roll the dough into an 18 x 13 inch rectangle about 1/4 inch thick. Trim the dough to make the rectangle as even as possible. Peel off the top piece of parchment place the jelly roll pan upside down over the circle of dough. Invert the pan and parchment with dough. Peel off parchment and settle the dough into the pan. (If it cracks a bit just use your fingers to press the dough back together. You can also use extra dough to patch holes if necessary.) Trim the edges of the dough so that it overhangs the side of the pan by no more than 1/2 inch.

Take a scrap of the dough and roll it into a rope approximately 6 inches long. (If there are no scraps use a bit of the second piece of dough). Use the rope of dough to wall off a section in the top left corner of the pan that is approximately 3 inch by 3 inches. Gently pinch the rope of dough so that it attaches to the bottom crust and rises up into a flat wall of crust. (The picture above shows how it should look).

In a small bowl combine the blueberries, 3 tablespoons of sugar, 2 teaspoons of corn starch, and a teaspoon of lemon juice. Stir gently until well mixed. Spoon the berry mixture into the walled off square at the top of the pie (this is the blue section of the flag). Place the raspberries, remaining sugar, cornstarch, lemon juice, and salt in a large bowl and stir gently until well mixed. Spread the raspberries evenly over the rest of the pan.

Remove the smaller piece of dough from the refrigerator and transfer it to a lightly floured piece of parchment paper. Top with an additional sheet of parchment and roll the dough into a rectangle that is just slightly longer than the length of the pan (about 16 inches long). Cut the dough into one inch strips. Carefully transfer the strips to the top of the baking pan to make the stripes (a long pastry spatula is great for this). Attach the edges of the dough stripes to the dough on the side of the pan. If the dough breaks when it is being transferred to the pan simply place the two pieces individually and press them together in the pan. Trim any excess length. There will be some extra dough. Roll out a bit of the extra dough and use a small star shaped cookie cutter to cut out dough stars. Scatter the dough stars over the blueberry section.

Brush the crust stripes with water and sprinkle with the remaining granulated sugar.

Bake the pie for 40-45 minutes or until the filing is bubbling and the crust is lightly browned.

The pie is best if served the day it is made.