Remove one disc of pie crust from the refrigerator, roll it out, and line a 9" plate with the crust.
Place pie plate in the refrigerator to chill while you prepare the lattice strips.
Roll the second disc of pie crust into a 12" circle. I prefer to use a tape measure or ruler here so I can make it as exact as I can. I also like to do this on a large circular surface (like a pizza stone) that I can place in the fridge if the butter/shortening starts to melt too much.
Use the measuring tape or ruler and a sharp knife to mark off 1" increments across the diameter of the pie crust. Turn your measuring device 90º and use your knife or a pizza cutter (my preference) to cut a straight line along each of the tick marks. You should now have 12 strips of dough. If the butter/shortening seems like it melted from a lot of touching, place the large round surface in the refrigerator for 10 minutes to firm up.
Pour your pie filling into the prepared pie plate and spread it out evenly.
Place the strips of pie dough parallel in front of you. Starting with the left-most strip, number this one #1 (either mentally or with a piece of tape on whatever surface you're working on). Working to the right, number each strip until you have numbered all 12 strips.
Picking up every other 1" strip (2, 4, 6, 8, 10, 12), lay 6 strips vertically and evenly spaced on top of the filled pie. The longer strips will be in the center of the pie and the shorter strips will be on the ends of the pie.
Fold every other strip (2, 6, and 10) away from you, slightly past halfway so they’re lying on top of themselves. Pick up strip #7 and lay it on the pie perpendicular to the folded strips slightly off-center. Unfold strips 2, 6, and 10 back over the pie and the strip you just lay, then fold back 4, 8, and 12 and repeat with strip #5, working toward yourself/toward the closer side of the pie. Fold 2, 6, and 10 back again, and repeat with strip #3. You now have a lattice top on half of the pie.
Working toward the other side of the pie in the opposite direction, fold strips 2, 6, and 10 toward you, then lay strip #9 across the pie. Fold back 4, 8 and 12 and repeat with strip #11, working away from yourself/toward the far side of the pie. Fold 2, 6, and 10 back one last time and finish with strip #1, if needed. I often don't use the very last strip, only because I like to space my lattice out a bit more to see the filling. Depending on how tight you lattice your strips, you may have space for it. If not, just discard or pinch into a thin spot on the edges before fluting.
Do not cut off excess pie dough. Instead, gather and pinch together the top strips with the bottom crust, then flute the edges. Allow the pie to chill in the refrigerator for 30 minutes.
When the pie has about 15-20 minutes left to chill, move a rack in the oven to the center position and preheat the oven according to your instructions.
Brush the whole pie with the egg wash, then sprinkle with coarse sugar. Place the pie on a large baking sheet (to catch drippings) and place the baking sheet with the pie on it in the oven to bake for the time suggested in your recipe.