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1
Preheat oven to 350u00b0F with rack in middle. Butter cake pan, then line bottom with a rectangle of parchment paper and butter parchment. Dust with flour, knocking out excess.
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2
Sift together cake flour, baking powder, baking soda, and salt.
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3
Beat together butter, sugar, and vanilla with an electric mixer at high speed until pale and fluffy, 3 to 5 minutes. Beat in eggs, 1 at a time, at medium speed. At low speed, mix in flour mixture in 3 batches, alternating with yogurt, beginning and ending with flour mixture, and mixing until just combined. Spread batter evenly in pan and rap pan on counter several times to eliminate air bubbles.
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4
Bake until cake pulls away from sides of pan and a wooden pick inserted in center comes out clean, 35 to 45 minutes. Cool in pan 10 minutes, then run a knife around edge. Invert onto a rack and discard parchment. Cool completely, about 1 hour.
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5
Stir together currants, 2 cups raspberries, sugar, and 1/8 teaspoon salt in a medium saucepan and let stand until juicy, about 15 minutes. Simmer, stirring occasionally, until fruit breaks down, about 8 minutes. Force through a fine-mesh sieve into a bowl, discarding solids. Cool sauce.
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6
Stir together confectioners sugar, corn syrup, cream, and vanilla until smooth.
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7
Put cake on a platter and spread icing on top in a thick layer, letting it run down sides. Let icing set at least 15 minutes. Serve with sauce and remaining 2 cups raspberries on the side.
