2 ounces unsweetened chocolate |
1 stick (1/2 cup) unsalted butter |
3 tablespoons unsweetened cocoa powder (not dutch-process) |
1/2 cup passover cake meal |
2 large eggs |
1 cup sugar |
1 1/2 tablespoons sour cream |
1/2 cup semisweet chocolate chips |
1/2 cup chopped walnuts (optional) |