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1
Position rack in center of oven and preheat to 350F.
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2
Butter 9-inch-diameter springform pan with 3-inch-high sides.
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3
Line bottom with waxed paper round.
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4
Finely grind walnuts with flour in processor; set aside.
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5
Stir chocolate in top of double boiler over simmering water until melted and smooth.
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6
Remove chocolate from over water.
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7
Cool chocolate slightly.
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8
Using electric mixer, beat butter and 7 tablespoons sugar in large bowl until light and fluffy.
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9
Beat in melted chocolate.
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10
Add yolks 1 at a time, beating well after each addition.
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11
Continue beating until smooth and light, about 3 minutes.
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12
Mix in ground walnut mixture.
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13
Using electric mixer fitted with clean dry beaters, beat whites in another large bowl until beginning to form soft peaks.
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14
Gradually add remaining 7 tablespoons sugar and beat to soft peaks.
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15
Stir 1/4 of whites into batter to lighten.
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16
Fold in remaining whites.
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17
Pour batter into prepared pan; smooth top.
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18
Bake until tester inserted into center comes out with some moist crumbs attached, about 40 minutes.
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19
Cool cake in pan on rack 10 minutes.
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20
Run sharp knife around pan sides to loosen cake.
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21
Release pan sides and cool cake completely (cake may fall as it cools).
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22
(Can be prepared 2 days ahead.
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23
Cover and let stand at room temperature.)
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24
Transfer cake to platter.
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25
Sift powdered sugar over cake.
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26
Cut into wedges and serve.
