First, set your oven to 350°F (175°C). Line your baking sheets with parchment paper or a silicone mat. Prepping them in advance makes baking so much smoother.
In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt. Whisking helps everything distribute evenly so you don’t get pockets of cocoa or baking soda in the dough.
In a larger bowl, beat the softened butter and sugar with your mixer for 2–3 minutes until light and fluffy. This step traps air, making your cookies soft inside. Add the egg and vanilla, and mix until smooth.
Slowly add the dry ingredients to the wet mixture. Use low speed so you don’t overwork the dough. The dough should be thick but easy to scoop.
Wrap the dough in plastic wrap and chill it for at least 30 minutes. Chilling prevents the cookies from spreading too thin and helps them bake into soft, chewy rounds.
Take about 1 tablespoon of chilled dough and roll it into balls. Coat each ball in granulated or decorative sugar for that sparkly finish. Place them on your baking sheet with space in between.
Bake the cookies for 10–12 minutes, until they puff up slightly but are still soft in the center. Don’t wait for them to look completely baked—they’ll firm up as they cool.
Let the cookies rest on the baking sheet for 5 minutes before transferring them to a cooling rack. This keeps them soft without falling apart.