Preheat your oven to 350°F (175°C). In a medium bowl, whisk together the all-purpose flour, baking powder, salt, and pumpkin pie spice until well combined. Set this mixture aside for later use.

In the bowl of a stand mixer fitted with the paddle attachment, or using a handheld electric mixer in a large bowl, combine the Crisco all-vegetable shortening and white sugar. Beat on high speed until the mixture becomes light and fluffy, about 3 to 5 minutes, scraping down the bowl as needed. Add in the egg, whole milk, and vanilla extract, beating until fully incorporated. Reduce the mixer speed to low and gradually add the dry ingredient mixture from Step 1, mixing just until combined. The dough will be slightly crumbly but will easily come together when pressed.

Lightly flour your hands and divide the dough from Step 2 in half. On a lightly floured work surface, roll each half out to 1/4-inch thickness for crispier cookies, or 3/8-inch thickness for softer cookies. Use 3-inch candy corn and pumpkin-shaped cookie cutters to cut out the dough. Carefully transfer the cookies, placing them 2 inches apart on prepared baking sheets. Bake one sheet at a time for 10 to 11 minutes, or until the cookies are puffed up and golden brown at the edges. Allow them to cool on the baking sheet for 2 minutes before moving to a wire rack to fully cool. I like to let the cookies cool completely before decorating so the icing doesn't melt.

In a medium bowl, whisk together sifted powdered sugar, warm water, salt, and food coloring if desired. Adjust consistency as needed: add more confectioners' sugar if the icing is too thin, or add a splash more water if it's too thick for piping. Pour the prepared icing into a piping bottle or bag. This simple icing is great for a base coat or easy cookie decorating.

In the clean bowl of a stand mixer fitted with the whisk attachment, or using a handheld electric mixer, beat the lemon juice and egg whites together on low speed until just combined. Gradually add in sifted powdered sugar, about 1/2 cup at a time, beating well after each addition until a smooth and spreadable frosting forms. Divide the royal icing into several bowls and color each as needed using food coloring. For a more vivid look, I like to use gel food colors—they really make the cookies pop!

Once the cookies from Step 3 are completely cool, decorate them using the prepared icing from Step 4 and/or royal icing from Step 5. Pipe, flood, or detail the cookies as desired, using multiple colors for creative designs.