Preheat your oven to 350° and line two baking trays with parchment paper. (Never skip your parchement paper!)
In a medium bowl, sift together the flour, salt, and baking powder. Set aside.
In a sauce pan, or in short bursts in the microwave, melt together the chocolate, espresso powder (if using) and butter.
With an electric mixer, whip together the eggs and sugar until pale yellow and very fluffy. At least 3 minute. If the color hasn't changed, it hasn't gone long enough.
Turn off the mixer, add in vanilla extract. Next, with a spatula, slowly mix the chocolate mixture into the eggs and sugar. Mix until just combined.
With a cookie scoop, or spoons, portion out roughly 2-3 tablespoons of the cookie dough.
Baker for 10-12 minutes until slightly domed. Cookies will fall and crackle more as they cool. Sprinkle with course salt, optional.