Preheat the oven to 450°F. Line a small baking sheet (a 9x13 - quarter sheet pan works well) with parchment paper.

Add the flour, granulated sugar, baking powder, kosher salt, and ground nutmeg to a medium or large mixing bowl. Whisk to combine.

Slice the butter-flavored shortening into cubes. Add the shortening cubes to the flour mixture. Use a pastry cutter, or a fork, to work the shortening into the flour. Keep working until the shortening is like large grains of sand, or crumbs. (If you prefer, you can also use a food processor to do the work.)

Make a “well” or indentation in the flour and shortening. Add the buttermilk and beaten egg. Stir to completely combine. The dough will be sticky.

Generously flour your work surface. Scoop your dough on top of the floured surface. Sprinkle a generous amount of flour on top of the dough.

Fold the flour into the sticky dough. Continue folding just until the dough is no longer sticky, but be careful not to work the dough too much. This could give you a tough shortcake.

Once the dough is no longer sticky, roll it out to 1-inch thickness using a rolling pin. Cut out 6 shortcake rounds using a round 3-inch cookie or biscuit cutter.

Place the rounds on the prepared cookie sheet about 1 inch apart.

Beat together the remaining egg and 1 tablespoon of water. Use a pastry brush to brush the tops of each shortcake with the egg wash.

Sprinkle about ⅛ teaspoon of granulated sugar on top of the shortcake rounds. Bake for 12-15 minutes, or until the tops and bottoms are a deep golden brown. Remove from the oven and allow the shortcakes to completely cool.

While the shortcakes are cooling, add the sliced peaches to a medium-sized (2-3 quart) bowl. Sprinkle the peaches with the granulated sugar and lemon juice. Stir until the peaches are completely coated.

Once the shortcakes are cooled, slice open a shortcake. Top the bottom of the shortcake with the sliced peaches. Add a dollop of thawed whipped topping, place the other half of the shortcake on top, and enjoy.