It only seems fitting to make a pie for Pi Day, right? Celebrate with a mixed berry treat that's decorated with the Pi symbol. It's nicely tart but still sweet as pie, and once cooled it slices perfectly every time.
Ease one disc of pie dough into an ungreased 9-inch pie pan. Refrigerate while you prepare the filling.
Combine the brown sugar and lemon zest in a medium bowl. Rub together until fully incorporated. Add the cornstarch, nutmeg and salt and mix well. Add the raspberries, blackberries and blueberries and gently toss to coat with the sugar mixture. Set aside.
To make a stencil, print out a Pi symbol that is about 4 1/2 by 5 1/2 inches. Trace the symbol onto the back of a paper plate. Cut out the symbol. You now have your template.
Place a disc of dough on a lightly floured surface. Lightly flour the pie crust and place the template in the center. Cut out the Pi symbol and remove it carefully from the disc. Leave the remaining dough on the work surface.
Add the lemon juice to the bowl of berries and gently toss until incorporated.
Remove the pie pan from the refrigerator and spoon the berry mixture into it. Top the pie with the disc of dough you cut the Pi symbol from. Seal the edges and use a paring knife trim away any excess dough. Place the pie in the freezer.
Preheat the oven to 400 degrees F. Lightly dust your work surface again with flour if needed. Place the third disc of dough on the surface. Punch out six each of the following, making the digits about 2 inches high: 3 •̣ 1 4.
Make an egg wash by beating the egg and 1 tablespoon water until smooth in a small bowl. Remove the pie from the freezer and brush the top with the egg wash. Place the numbers and dots around the edges of the pie in this order 3 • 14, repeating until you have used them all. Brush the top with egg wash again.
Place the pie pan on a baking sheet. Bake until the crust is golden brown and the filling is bubbling, about 50 minutes. Allow the pie to cool completely on the sheet pan before slicing.