In a medium mixing bowl, sift or whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
In a large mixing bowl, beat together the butter and both sugars until light and creamy. This will take about 3 minutes if using an electric mixer or 5 to 6 minutes if creaming by hand.
Add the eggs and vanilla, and beat to combine. Add the buttermilk and dry ingredients in alternating batches, beating until incorporated.
Preheat the oven to 350°F. Line a cookie sheet with parchment paper.
Using a medium cookie scoop, scoop the batter, placing 2 inches apart on the prepared cookie sheet.
Bake for 13 to 14 minutes, until the tops are puffed up & slightly cracked.
Let the cookies rest on the cookie sheets for 5 minutes before transferring them to wire racks to cool completely.