Preheat oven to 325 degrees. Mix flour, baking powder and salt together. Set aside. Using an electric mixer, whip eggs for 1 minute. Add sugar, peppermint extract and espresso and whip on high speed for 15 minutes or until mixture is thick. While eggs are whipping, melt bittersweet chocolate and butter together in a bowl in a water bath.
Fold chocolate mixture into egg mixture until partially combined, as there should still be some visible streaks. Carefully fold flour mixture into batter, then add chocolate chips and almonds. If batter is runny, let it rest for about 5 minutes to thicken.
Scoop generous teaspoonfuls of batter onto a parchment-lined baking sheet. Bake for 10 to 13 minutes or until cookies puff and are cracked on top. Allow cookies to cool before removing from baking sheet.
Note: In place of espresso, you may substitute an instant coffee extract (for example, 5:1 ratio of instant coffee to water).
Chef's tips: Use a powerful stand mixer (such as a Kitchen Aid) rather than a hand-held electric mixer and be sure to whip the egg/sugar mixture on high speed long enough for it to reach a thick ribbon stage. It's best to add the chocolate/butter mixture to the egg mixture while it is still warm. Note that the cookies don't "puff" tremendously to indicate doneness, so be careful not to overbake.