Preheat your oven to 350°F (175°C). Line a baking sheet with parchment or a silicone mat—this helps cookies brown evenly without sticking.

In a medium bowl, whisk together flour, cocoa powder, baking soda, and sea salt. Give it a good mix so no cocoa clumps remain. That way every bite tastes consistent.

In a large mixing bowl, beat the softened butter with granulated sugar and brown sugar until light and fluffy—about 2–3 minutes using a stand mixer or hand mixer. You’re looking for a ribbon-like hold when the beater lifts.

Crack in the egg and extra yolk, then pour in vanilla extract and Greek yogurt. Mix on low until just combined—don’t overmix, or cookies can get cakey instead of chewy.

Switch to a spatula and gently fold the dry ingredients into the wet mixture. Stop once you see no streaks of flour—overworking builds gluten, which makes cookies tough.

Stir in both semi-sweet and milk chocolate chips. For a fun twist, reserve 10% of the chips to press on top of each dough ball before baking—this gives a bakery-style finish.

Scoop heaping tablespoons of dough (about 2 tbsp each) onto a plate, cover, and chill in the fridge for 20–30 minutes. Chilling firms up the butter and prevents cookies from flattening into thin crisps.

Place dough balls 2 inches apart on the prepared sheet. Bake for 10–12 minutes—edges should look set while centers remain soft. Rotate the pan halfway if your oven has hot spots.

Let cookies rest on the sheet for 5 minutes before transferring to a wire rack. This short cooling locks in moisture and helps cookies finish cooking without getting dry.