**Preheat Oven:** Preheat your oven to 350°F. Line two baking sheets with parchment paper and set aside.

**Cream Butter and Sugars:** In a large bowl, cream together the softened butter, light brown sugar, and granulated white sugar with an electric mixer for about 2 minutes, until light and fluffy.

**Add Egg Yolks and Vanilla:** Mix in the egg yolks and vanilla on medium speed for about 2 minutes, until the mixture is pale and fluffy.

**Combine Dry Ingredients:** Add the flour, cocoa powder, salt, baking powder, and baking soda to the bowl. Mix until combined.

**Add Chocolate Chips:** Stir in the chocolate chips until just incorporated.

**Scoop Dough:** Scoop the dough into 18 balls. Arrange the dough balls two inches apart on the prepared baking sheets.

**Bake Cookies:** Bake the cookies for 10-12 minutes. Bake for a shorter time for slightly underdone centers, or the full time for crispier edges.

**Cool and Sprinkle with Salt:** Remove from the oven and, if desired, sprinkle with flaky sea salt. Let the cookies cool on the baking sheet for 5 minutes before transferring them to a cooling rack to cool for an additional 5 minutes.

**Store Leftovers:** Store any leftovers in an airtight container for up to four days.