Optional: chopped walnuts, pecans, hazelnuts or peanuts
1/4 cup semisweet chocolate chips
1 teaspoon canola oil
Preheat oven to 350°. In a large bowl, beat the eggs, oil, sugar, water and vanilla. Whisk together the flour, cocoa, salt, baking powder and, if desired, espresso powder; stir into egg mixture until blended.
Spread into a greased or parchment paper-lined 15x10x1-in. baking pan. Top with chopped nuts if desired. Bake until very firm to the touch, 12-15 minutes. Cool on a wire rack. Break into pieces. In a microwave, melt chocolate chips and oil; stir until smooth. Drizzle over pieces. Let stand until set before cutting.