Weigh or measure your sugar into a bowl and set it aside. Next, weigh or measure the flour, salt, baking powder, cocoa powder into a bowl and run a whisk through to blend.
Cream the butter and sugar together till light and fluffy, about 2 to 3 minutes. Next, add the vanilla extract and the egg. Finally, add your dry ingredients and mix until combined.
Place the dough on a pastry sheet and divide it in half. Flatten each cookie dough half before wrapping it in plastic wrap, then refrigerate for 30 minutes.
Now, please take one of the chilled cookie disks out and place it onto a lightly floured pastry mat. I made my cookies about ⅛" thick. There are bands on the ends of my rolling pin so that you can roll out the dough evenly. If you roll out your dough thicker, you may need to add a minute or two to the time. Next, cut out heart-shaped cookies (I used three different sizes) and place them on a parchment-lined sheet pan. They are ready for the oven.
Bake at 350°F (175°C or 180°C) for 7-9 minutes. After baking, leave the cookies on the pan for a minute before moving them to a cooling rack.