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1
In a medium bowl, sift together the flours, baking powder, baking soda and salt.
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2
In the bowl of a stand mixer using the paddle attachment, or in a large bowl using a hand mixer, cream together the butter and sugar at medium speed until the mixture is light and airy, about 5 minutes.
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3
Scrape the sides as needed for even mixing.
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4
With the mixer running, mix in the whole eggs, then the yolks, one at a time, until fully incorporated.
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5
Mix in the vanilla until just combined.
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6
Mix in the combined dry ingredients and sour cream, alternating between the two (one-third of the dry, then half of the sour cream, in stages) until both are thoroughly combined, being careful not to over-beat.
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7
Evenly spoon the batter into 20 lined cupcake pans; the batter should fill each liner two-thirds to three-fourths full.
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8
Bake the cupcakes, one pan at a time and in the center of the oven, until the cupcakes have risen and a toothpick inserted into the center comes out clean, 15 to 20 minutes.
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9
Rotate the pan halfway through for even baking.
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10
Remove the pan to a rack to cool before frosting the cupcakes.
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11
The cupcakes are best eaten the same day they are made or frozen as soon as they are cool.
