Heat oven to 375 degrees F. Line baking sheets with parchment paper.

Whisk together the flour, baking powder and salt in small bowl until well blended.

Lightly beat the eggs in large bowl. Add the sugar, coffee and vanilla; beat with hand-held mixer on high speed for 10 minutes or until tripled in volume.

Meanwhile, heat together butter, bittersweet chocolate and unsweetened chocolate in top of double boiler over simmering water until butter and chocolate are melted. Remove top of double boiler from over water. Stir mixture until smooth.

Gently fold chocolate mixture into egg mixture until partially combined; some streaks should remain. Fold in flour mixture. Fold in chocolate chips. Let batter rest 10 minutes; batter will thicken slightly.

Drop the batter by heaping teaspoonfuls onto the prepared baking sheets, spacing the batter mounds about 2 inches apart.

Bake in 375 degrees F oven until the cookies are puffed and cracked, 8 to 9 minutes. Cool cookies on baking sheet on wire rack for 5 minutes. Remove cookies to rack and let cool completely. Variation: Substitute 1/2 cup chopped toasted nuts or dried sour cherries for 1/2 cup of the chocolate chips.