Slice the yellow squash into rounds, remove the seeds, and grate or finely chop until you have about 2 cups. Cook the grated squash in a pot of boiling salted water for 8-10 minutes until very tender, then drain thoroughly in a colander, pressing gently to remove excess moisture. Mash the cooked squash until completely smooth, then set aside to cool slightly. Removing excess moisture is key here—too much liquid will make the pie soggy, so don't skip this step.

Preheat your oven to 350°F. Remove the pie crusts from the refrigerator and let them come to room temperature for a few minutes for easier handling. Place one crust into a 9-inch pie dish, gently pressing it into the bottom and sides. Set the other crust aside for the top layer. Do not pre-bake the crusts—we'll bake everything together to develop a golden, flaky texture.

In a large mixing bowl, cream together the softened butter and sugar until light and fluffy, about 2-3 minutes. Add the room-temperature eggs one at a time, beating well after each addition to ensure proper emulsification—this creates a smooth, custardy filling. Stir in the flour and ground nutmeg until just combined, then fold in the cooked mashed squash from Step 1, vanilla extract, lemon juice, and shredded coconut until everything is evenly distributed. I like to use fresh lemon juice rather than bottled for its brighter flavor, which really complements the sweetness of the squash.

Pour the filling mixture from Step 3 into the prepared pie crust from Step 2, spreading it evenly. Carefully place the second pie crust on top, then crimp the edges with a fork or your fingers to seal the two crusts together. You can make small slits in the top crust with a knife to allow steam to escape during baking and prevent the crust from puffing up too much.

Place the assembled pie in the preheated 350°F oven and bake for 40-45 minutes, until the crust is golden brown and the filling is set but still slightly jiggly in the very center when you gently shake the pie. If the crust edges are browning too quickly, tent them loosely with aluminum foil halfway through baking. The pie will continue to set as it cools, so don't overbake it or the texture will become too firm and dense.

Remove the pie from the oven and let it cool at room temperature for at least 30 minutes before slicing. This resting time allows the custard filling to firm up properly and makes for cleaner slices. The pie can be served warm or chilled, depending on your preference. Store any leftovers covered in the refrigerator for up to 3 days.