Heat the oven to 350°F (177°C). Line baking sheets with parchment paper or silicone mats and set aside.
Whisk the flour, baking powder, and salt together in a medium bowl until evenly distributed; set this dry mix aside.
In a large mixing bowl, beat the vegetable shortening and granulated sugar with a hand mixer or stand mixer fitted with a paddle on medium speed until lightened and slightly fluffy, about 1 to 2 minutes.
Add the egg, milk, vanilla, and almond extract to the shortening-sugar mixture and mix on low until incorporated, then increase speed for 10–15 seconds to fully emulsify. Scrape the bowl sides with a spatula.
With the mixer on low, gradually add the dry ingredients and mix just until a cohesive dough forms. The dough may look crumbly at first but will come together — finish by pressing it with your hands into a smooth ball.
Divide the dough in half. Place one half between two large sheets of parchment paper and roll to about 1/4-inch thickness. Repeat with the second half. If the dough feels soft, transfer the rolled sheets to a baking sheet and chill for 20–30 minutes — chilled dough cuts cleaner and keeps cookie edges sharp.
Remove the top sheet of parchment and use 3–4 inch Halloween cookie cutters to stamp shapes. Transfer cut cookies to the prepared baking sheets using a thin spatula; re-roll scraps once and repeat. Arrange cookies about 1 inch apart.
Bake in the preheated oven for 10–12 minutes, rotating the pans halfway if you have multiple sheets. Cookies should be set on top and just starting to color on the bottom edges.
Let the cookies cool on the baking sheet for 5 minutes to firm up, then transfer to a wire rack to cool completely before icing (warm cookies will make the icing slide).
Prepare your icing to a medium flood consistency (it should hold a ribbon when lifted and smooth out in 10–15 seconds). Divide into bowls and color with gel paste: reserve a larger portion for base colors and small amounts for details.
Fit piping bags with small round tips (or snip the corner). Outline each cookie in the desired color, then flood the center. Use a scribe tool or toothpick to spread icing into corners and pop air bubbles. Add details (eyes, stems, buckles) once the base has set slightly, or pipe them on while still wet if you want the colors to blend.
If adding sprinkles, do so immediately after flooding so they adhere. Allow iced cookies to dry at room temperature for several hours — ideally overnight — before stacking or packaging.