Be sure to freeze your butter and shortening in advance!

In a medium bowl, whisk together the gluten-free flour, sugar and salt.

In a small measuring cup, add the egg and vinegar. Whisk until completely smooth, then add cold water until the mixture measures ½ cup and whisk to fully combine. Refrigerate the egg-vinegar mixture until ready to use.

Using the large holes of a box grater, grate the butter. Add the grated butter to the dry ingredients and toss to coat in the flour mixture.

Using the large holes of a box grater, grate the shortening. Add the grated shortening to the dry ingredients and toss to coat in the flour mixture.

Drizzle 1 tablespoon of the egg-vinegar-water mixture over the flour and butter mixture. Using a rubber spatula, gently stir and toss the mixture, distributing the moisture evenly. Continue adding the liquid, 1 tablespoon at a time, stirring after each addition, until the dough begins to come together in large clumps. Repeat until you’ve added 5-6 tablespoons of the liquid. (Note that you will only use about ½ of the liquid.)

Pour the dough into a bowl and use your hands to gently bring the dough together, being careful not to overwork it. Add another tablespoon of liquid if needed. Don’t be tempted to add too much liquid! It should be moist enough to hold together when pressed but not sticky.

Turn the dough out onto a lightly floured surface. Gather it together with your hands, pressing any loose bits into the dough to form a cohesive ball.

Gently shape it into a disc about 1 inch thick. Wrap the disc tightly in plastic wrap and refrigerate for 1 hour or up to 2 days.

If the dough has been in the refrigerator longer than 1 hour, let the dough sit at room temperature for 15 minutes before rolling.

Place the dough on a lightly floured pastry mat or a silicone baking mat. Roll the pie crust into a circle 12 inches in diameter. You may need to press it together if it starts to slit or break on the edges. This is normal; gluten-free pie crust requires a bit of patience to roll out.

After rolling, use the pastry mat to flip the dough into a 9-inch pie plate. Gently ease the dough into the edges of the pan. Trim any excess edges with scissors and shape the edges as desired.

Wrap the shaped pie crust loosely in plastic and place in the freezer for 15 minutes or up to 1 hour until chilled and firm. With a fork, prick holes all over the bottom and sides of the crust.

Place a pizza steel in the oven. (A pizza steel helps to ensure a crispy bottom crust.) Preheat the oven to 375°F.

Line the frozen crust with parchment paper and pie weights. Bake 10 minutes. Carefully remove weights and parchment. Let the crust cool 10 minutes on a rack. Reduce oven temperature to 350°F and keep the steel in place.

In a large bowl, whisk the melted butter and sugar. Add the eggs one at a time, whisking well after each.

Sprinkle in the flour, lemon zest, and nutmeg and whisk to combine.

Whisk in the buttermilk, lemon juice, and vanilla until smooth.

Place the pie dish on a rimmed baking sheet. Pour in the filling. Sprinkle the top lightly with nutmeg.

Bake at 350°F for 50 to 55 minutes, until the edges are set and puffed and the center has a slight wobble.

Cool on a rack until room temperature, 2 to 3 hours. Serve at room temperature or place in the fridge.