1. Preheat oven to 350ºF. Line 2 large baking sheets with parchment.

2. In a bowl over simmering water, melt chocolate chips. Remove from heat.

3. Sift flour, cocoa, espresso, baking powder and salt. Using an electric mixer on medium-high speed, beat butter and sugar until light, about 2 minutes. Beat in eggs, then vanilla. Stir in melted chips. Fold in flour mixture and white chocolate chips.

4. Put tablespoonfuls of dough on baking sheets 2 inches apart. Bake until tops are cracked, about 15 minutes total. Repeat with remaining dough.