In A Large Bowl, Beat The Butter, Granulated Sugar, And Brown Sugar On Medium Speed Until Light And Fluffy, About 2-3 Minutes.

Add The Egg And Vanilla Extract, Mixing Just Until Combined.

In A Separate Bowl, Whisk Together The Flour, Baking Powder, Baking Soda, Salt, And Cocoa Powder If Using.

Gradually Add The Dry Ingredients To The Wet Ingredients, Mixing On Low Speed Until Just Combined. Do Not Overmix.

Flatten The Dough Into A Disk, Wrap It In Plastic Wrap, And Chill In The Refrigerator For At Least 1 Hour (Up To Overnight).

Preheat The Oven To 350°F (175°C). Line Baking Sheets With Parchment Paper Or Silicone Baking Mats.

On A Lightly Floured Surface, Roll Out The Dough To About 1/4-Inch Thickness. Use Halloween-Themed Cookie Cutters To Cut Out Shapes.

Place Cookies 2 Inches Apart On Prepared Baking Sheets. Bake For 8-10 Minutes, Until The Edges Are Set But Centers Still Look Slightly Underbaked.

Allow Cookies To Cool On The Baking Sheet For 5 Minutes, Then Transfer To A Wire Rack To Cool Completely.

Once Cooled, Decorate With Royal Icing Or Sugar Cookie Frosting. Add Sprinkles, Candy Eyes, Or Chopped Candies While Icing Is Still Wet For Best Adhesion.