Start by adjusting the oven rack to the second level (just above the center) and preheat your oven to 350ºF. Line two baking sheets with parchment paper or silicone mats and set aside.

In a medium bowl, mix together the all-purpose flour, baking powder, and salt. Set it aside for later use.

In a large mixing bowl, beat the eggs, egg yolk, granulated sugar, vegetable oil, and vanilla extract using a hand mixer or stand mixer on medium-high speed until everything is well combined and frothy.

While that’s happening, melt the semi-sweet chocolate chips and unsalted butter together in a small saucepan over medium heat until they’re smoothly combined. Once melted, remove from the heat and mix in the unsweetened cocoa powder and espresso powder, if you’re using it.

Pour the melted chocolate mixture into the bowl with the wet ingredients and gently mix until the chocolate is just combined.

Gradually add the dry ingredient mixture to the wet ingredients, mixing on low speed until just incorporated. The batter should be somewhat thinner, yet still scoopable.

Using a cookie scoop or two spoons, drop spoonfuls of cookie dough onto the lined baking sheets, spacing them about 1.5 inches apart.

Sprinkle sea salt flakes on top of each cookie, then pop them in the oven to bake for 8 to 10 minutes, or until they have a shiny, crackly surface.

Once baked, you can add a few extra chocolate chips on top right away for that gorgeous finishing touch. If you want them to be perfectly round, use a cookie cutter immediately after they come out of the oven!

Allow the cookies to cool on the baking sheets for about 5 minutes before transferring them to a rack to cool nearly completely. They're delightful warm, so enjoy! Keep any extras in an airtight container at room temperature for up to 2 days!