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1
Preheat oven to 350F.
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2
Butter and flour 15 x 10 x 1-inch jelly-roll pan.
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3
Stir chocolate and butter in heavy medium saucepan over medium-low heat until melted and smooth.
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4
Remove from heat.
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5
Combine sugar, eggs and salt in heavy large saucepan.
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6
Whisk constantly over low heat just until sugar dissolves, about 5 minutes (do not boil).
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7
Remove from heat.
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8
Whisk in chocolate mixture and vanilla.
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9
Whisk in flour and nuts.
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10
Spread batter in pan.
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11
Bake until tester inserted into center comes out with some moist crumbs still attached, about 30 minutes.
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12
Cool brownies completely in pan on rack.
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13
Stir semisweet chocolate in top of double boiler over barely simmering water until smooth.
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14
Remove from over water.
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15
Spread over brownie.
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16
Stir white chocolate in top of double boiler over barely simmering water until smooth.
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17
Spoon into resealable plastic bag.
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18
Cut very tip off 1 corner of bag.
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19
Pipe lines of white chocolate crosswise atop brownie, spacing lines 1 inch apart.
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20
Draw a toothpick lengthwise across lines, alternating direction from left to right and right to left, to create marbled pattern.
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21
Chill just until firm enough to cut, about 30 minutes.
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22
Cut into small squares.
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23
(Can be made 3 days ahead.
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24
Refrigerate in single layer in airtight containers.
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25
Bring to room temperature before serving.)
