This brownie recipe was designed with the chocoholic in mind. It features four kinds of chocolate: semi-sweet, unsweetened, cocoa and chocolate chips. The freshly ground pasilla negra chile enhances the chocolate and adds a mild hit of spiciness. Don't be tempted to substitute commercial chili powder or cayenne for the pasilla. If you're looking for a substitution, go with ancho chile powder which is readily available.
Preheat oven to 350 degrees. Place the rack in the middle position. Butter an 8-inch square baking pan. Line the pan with 2 pieces of parchment paper, leaving an overhang on all four sides to create a sling. Butter the parchment. Set aside.
In medium heatproof bowl set over a pot of simmering water, melt the butter, and both the chopped semisweet and unsweetened chocolates, stirring occasionally until smooth. Let cool slightly.
In a medium bowl, whisk together the flour, chile powder, cocoa and salt.
In another medium bowl, whisk together the eggs, both sugars and vanilla in a medium bowl until combined. Whisk in the warm chocolate mixture. Then switch to a rubber spatula to stir in the flour mixture and chocolate chips. Mix until just combined. Pour mixture into prepared pan and spread into corners. Bake until a toothpick inserted in the center comes out with a small amount of sticky crumbs clinging to it, 35 to 40 minutes. Cool completely on a wire rack. Lift the brownies out of the pan using the parchment paper overhangs and transfer to a cutting board to slice.
Stem and seed 3 pasilla chiles. Lay them on an ungreased baking sheet in a preheated 375 degrees oven for 4 minutes or until toasted and dry. Let cool and then grind in spice grinder. You should have about 2 1/2 tablespoons of pure chile powder.