Dark-Chocolate Chile Balls

1. Preheat the oven to 350°F. Line cookie sheets with parchment paper.
2. In a saucepan over low heat, melt the chocolate with the butter. Set aside to cool.
3. In a bowl, mix the flour, baking powder, salt, and chiles. In a separate bowl, beat the eggs, sugar, espresso powder, and vanilla at high speed for 2 minutes. Add the melted chocolate, beating to blend.
4. Add the flour mixture and stir until combined. Stir in the chocolate chips and walnuts.
5. The chocolate will begin to solidify, so immediately scoop dough by spoonfuls, shape into balls, and place about 2 inches apart on the cookie sheets.
6. Bake for 10 to 12 minutes, or until the cookies have a shiny skin and are slightly firm. Let them cool on the cookie sheets for several minutes, then transfer to a rack.

*Use ground dried chiles, not chili powder, which is a mixture of spices. Vary to your taste: Ancho chiles have a mild and smoky character; guajillos, more heat; and cayenne, a lot of heat but not much flavor. Chipotles give both heat and a smoky tang.