Preheat your oven to 350 °F (175 °C) and line a baking sheet with parchment paper.

In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.

In a large bowl, microwave the butter for 25–30 seconds until softened (not melted). Add both sugars and beat at low speed for 1–2 minutes until creamy.

Beat in the egg and vanilla just until combined—avoid over-mixing.

Gradually mix in the dry ingredients until the dough forms a ball that’s easy to roll.

Shape dough into balls (about 2 tablespoons each for ~15 cookies), place them an inch apart on the baking sheet, and gently flatten with your palm. Bake for 10–11 minutes. The centers should still look slightly soft; they’ll firm up as they cool.

Let cookies rest on the baking sheet for at least 5 minutes before transferring to a rack. Store in an airtight container at room temperature for up to 5 days.