Melt the chocolate and butter together over a double boiler until glossy and smooth, about 7 minutes. (See recipe notes in the text, above, for a double boiler how-to and how to use a microwave instead.)
Meanwhile, in the bowl of an electric mixer fitted with the paddle attachment, beat together the eggs and sugar over medium speed until thick and pale, about 5 minutes. Add the vanilla and salt. Gently stir the melted chocolate and butter mixture into the batter. Add the flour and baking powder and mix just until fully combined. Stir in the chocolate chips.
Scrape the dough into a shallow baking dish and freeze until well chilled and firm, about 1 hour.
Preheat the oven to 350°F and grease or line with parchment two half-sheet pans.
Scoop two-tablespoon sized mounds of cookie dough onto the baking sheets, leaving 2 inches of space between each cookie.
Bake 11 to 14 minutes, until the cookies look dry around the edge and cracked on top.
Cool for 10 minutes on the sheet pan, then transfer to a cooling rack to cool fully.Tip: These cookies will keep in an airtight container for up to 4 days, but will probably all be eaten well before that.
Disclaimer: Nutrition information is provided for courtesy purposes only, and is an estimate not verified by medical or nutrition experts. Read the full nutrition disclaimer.