Prepare the crusts, well one of them. Roll out half of the dough to a 1/8-inch-thick circle on a lightly floured surface, to about 13 inches in diameter. Fit the dough over a 9-inch pie pan, and trim the edges to a 1/2 inch over the edge all around the pan. Put into the refrigerator to chill for about 30 minutes.
Mix the blueberries, sugar, flour, cinnamon, salt, thyme, and lemon juice in a large bowl.
Transfer the filling to the chilled pie pan, returning the pan to the fridge when done.
Roll out remaining dough to the same size and thickness as the first. Using numbered cookie cutters, cut the number Pi into the crust. The quicker you do this the better; the number goes on forever, and you don’t want to overwork (or thaw out) your crust too much. Pi is 3.141592653589793238462643383279… you can see the full Pi number here. Trust me, the whole thing won’t fit.
Whisk egg and 1 tablespoon of water to make an egg wash. Brush the rim of the bottom crust with a bit of egg wash.
Place the cut crust on top of the berry filling. Tuck the top dough over and under the edge of the bottom dough, and crimp the edges with your fingers. Transfer the pie to the refrigerator to chill until the dough is firm, about 30 minutes. Heat oven to 425°F.
Bake 45 minutes at 425°. Transfer to a wire rack to cool. Let cool completely before serving.