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1
Preheat oven to 350F.
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2
Butter 2 (9- by 2-inch) round cake pans and line bottoms of each with rounds of wax or parchment paper.
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3
Butter paper and dust pans with flour, knocking out excess.
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4
Sift together flour, baking powder, baking soda, and salt.
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5
Beat together butter and sugar in a large bowl with an electric mixer until light and fluffy.
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6
Add eggs 1 at a time, beating well after each addition, then beat in vanilla.
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7
Add half of flour mixture and mix at low speed until just blended.
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8
Add sour cream, mixing until just combined, then add remaining flour mixture, mixing at low speed until batter is smooth.
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9
Divide batter between pans, smoothing tops.
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10
Bake in middle of oven until cake is springy to the touch and a tester comes out clean, 30 to 40 minutes.
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11
Cool in pans on racks 10 minutes, then invert onto racks, remove paper, and cool completely.
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12
Trim tops of cooled cake layers with a long serrated knife if necessary to make flat and level.
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13
Halve each layer horizontally with serrated knife to make a total of 4 layers.
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14
Put 1 cake layer on a cake plate and spread with 3/4 cup frosting.
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15
Layer remaining cake layers using 3/4 cup frosting between each layer.
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16
Frost top and sides of cake with remaining frosting.
