Here's what you'll need:
at least 1 disposable pizza pan (9" or bigger)
circle cutter (optional)
sweetened, condensed milk
The way in which we're going to commemorate π is with something I'm going to call a "pie circle". In other words, we're going to create a pie based on the design of a crop circle found in England in the middle of 2008. You can read all about that crop circle at this link:
Step 1: Start the Template
Cut an 8.5" circle from the center of the pizza pan. I used a circle cutter to "score" the rim of the circle, then a hobby knife to finish off any spots that weren't cut all the way through. Also cut the circle out of the graph paper; it should be about 8".
Tape the two circles together concentrically. I found it easier to cut the sections out of the template if I shaded in the parts to be cut first. Start by shading in the entire center two circles. Skip the next circle, then fill in three segments of the fourth circle, representing the 3 at the beginning of π. Skip the fifth circle, then fill in 1 segment, representing the 1 after the decimal. Continue in that fashion, skipping one circle between successive digits, until you hit the end of your graph paper. In my case, this was after the 9.
Step 2: Cut It Out!
Step 3: Making the Crust
Press the crust-to-be into a 9" pie plate. Be sure to go up the edges of the plate, but try not to get any crumbs on the rim. Bake the crust at 325°F for about 15 minutes, then cool on a rack for 20.
Step 4: Breaking Both Eggs and Rules
For the filling, mix four egg yolks together with the zest of two limes (regular, Persian limes) in a medium bowl. Stir in one can of sweetened, condensed milk (14 oz). Add 3 drops of green food coloring, and stir that in too. You can leave it out if you really want to, but I think it makes the pie look more like a barley field. Surprisingly, that's a good thing in this case.
Stir in 1/2 cup of lime juice, then let it sit for about 20 minutes. During that time it will get somewhat thicker; that's the acid from the lime juice thickening the proteins.
Step 5: Assembly
Spray your template with cooking spray. This will help when we remove the template later. (Don't do what I did #2: try not to spray vegetable oil all over your camera.)
Press the template gently into the pie. Don't press it in too much, but you do want to keep the template from bending up instead of sitting flat on the pie. Bake the pie at 325°F for about 15 minutes; it should be fully set, but still a bit jiggly in the center.
Step 6: The Reveal
Now comes the hard part. Using the tip of a knife, pull up the edge of the template. It should release from the pie without much effort. Continue pulling up the template, working evenly from both sides towards the center. The excess graham cracker crumbs will probably stick to the cooking spray on the top of the template, as long as there aren't too many, but do try to be careful not to spill them where they shouldn't be.
Lastly, we'll add a decimal point to our π. Dip the end of a drinking straw into a dish of graham cracker crumbs; you want to pick up enough crumbs to make a dot, but not so many that the dot will overflow into the rings. Keep the crumbs from falling out by covering the bottom end of the straw with a finger, then position the straw over the pie between the 3-segment ring and the first 1-segment ring. Remove your finger, letting the crumbs out.
Refrigerate the pie for a few hours or overnight, then serve and enjoy!