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1
Position rack in center of oven; preheat to 350F.
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2
Line an 8-inch-square baking pan with foil, letting it overhang on two opposing sides.
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3
Coat with cooking spray.
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4
Sift flour, confectioners' sugar and cocoa together into a small bowl.
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5
Combine the 3 ounces coarsely chopped chocolate and butter (or oil) in a heavy medium saucepan; place over the lowest heat, stirring, until just melted and smooth, being very careful the chocolate does not overheat.
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6
Remove from the heat and stir in granulated sugar, corn syrup mixture, vanilla and salt until the sugar dissolves.
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7
Vigorously stir in egg until smoothly incorporated.
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8
Gently stir in the dry ingredients.
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9
Fold in the walnuts (if using) and the remaining 2 1/2 ounces chopped chocolate just until well blended.
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10
Turn out the batter into the pan, spreading evenly.
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11
Bake the brownies until almost firm in the center and a toothpick inserted comes out with some moist batter clinging to it, 20 to 24 minutes.
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12
Let cool completely on a wire rack, about 2 1/2 hours.
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13
Using the overhanging foil as handles, carefully lift the brownie slab from the pan.
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14
Peel the foil from the bottom; set the slab right-side up on a cutting board.
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15
Using a large, sharp knife, trim off any dry edges.
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16
Mark and then cut the slab crosswise into fifths and lengthwise into fourths.
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17
Wipe the blade with a damp cloth between cuts.
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18
*To toast chopped walnuts, heat a small dry skillet over medium-low heat.
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19
Add nuts and cook, stirring, until lightly browned and fragrant, 2 to 3 minutes.
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20
**Store in an airtight container for up to 3 days or in the freezer for up to 2 weeks; as long as nobody knows about them.
