Forget the fireworks! This stunning, berry-filled pie is what will have your guests oohing and aahing this July 4th.
For the dough:
In a large bowl, whisk together the flour, sugar and salt. Toss in the butter and then toss some more to coat. Gently squeeze the butter, "smushing" it between your fingers to flatten. Continue "smushing" until all the larger pieces have been flattened slightly.
Mix together the water and lemon juice and pour the liquid over the dry ingredients. Using a wooden spoon or your hands, gently stir them together to distribute the liquid, pushing it up the side of the bowl to cause the butter to streak a bit. Gently fold over and press into a disk before turning out onto the workbench.
Roll out the dough into a 12- by 16-inch rectangle. Fold one of the shorter ends in towards the center line. Fold the other end over the first fold to complete a letter fold. Fold the bottom end up to meet the top. You should have a square shape. Wrap in plastic wrap and refrigerate for 10 minutes.
To roll out the dough and line the pan:
Divide the dough into two pieces so that you have one slightly smaller piece (for bottom crust) and one larger piece (for top crust options).
Sprinkle flour on your work surface, the top of the dough and your rolling pin. Working from the center out, start rolling gently up and then back to center and down, being careful not to roll over the edge. It will look almost square at this point. Rotate the dough a quarter turn and repeat the rolling. Continue turning and rolling the dough until you have a circle that is 1½-2 inches larger than your pan.
Transfer the dough to your pan, pressing it into the sides and bottom. Chill in the refrigerator or freezer for about 20 minutes to let the dough relax.
To blind bake the bottom crust:
Preheat the oven to 350°F. Dock the dough by using a fork to make pinprick holes along the bottom and sides of the dough. Trim the edges of the dough so that they come to the rim of the pan.
Line the dough with a generous sheet of parchment and weigh down with uncooked rice and beans or pie weights. Transfer to the oven and bake for 10 minutes. Remove the parchment and weights and continue cooking for about 10 minutes until the dough loses its raw sheen.
For the filling:
Grind the instant tapioca into a powdery form if it isn't already powdered. In a small bowl, stir together the sugar and the tapioca until well combined. Add the salt and nutmeg and stir to combine. In a separate bowl, toss the blueberries with 2 tablespoons of the mixture. In another separate bowl, toss the raspberries with the remaining sugar mixture. Let the berries sit for 10 minutes to allow the tapioca to absorb some of the juices.
Roll the remaining larger half piece of dough into a rectangle between 1/4- and 1/8-inch thick. Cut out five to six 10-inch strips of dough, each measuring about 1/2-inch in depth. Cut two in half so you're left with four 5-inch long strips. With the remaining dough, cut out stars (at least 13).
Place the prepared raspberries in the pie shell, leaving 1/4 of the shell at the upper left corner free, and place the prepared blueberries in the open 1/4 of the shell. Drape the 10-inch strips across the lower portion of the pie, across the raspberries, trimming when the pieces drape too far over the bottom crust.
Place the shorter strips over the upper right hand portion, avoiding the blueberries. Space all the strips evenly. Place 3 or 4 stars over the blueberry "field" and then place the remaining stars along the perimeter of the crust, gluing them down with the egg wash.
Egg wash the stars and stripes and sprinkle with Swedish pearl sugar.
Bake the pie until the lattice strips turn flaky and start to brown and the berries are bubbling, about 25-30 minutes.