FOR THE CAKE: Cream the butter and sugar in the bowl of an electric mixer fitted with the paddle attachment on high speed for 4 to 5 minutes, until light. Reduce the speed to low and add the eggs 1 at a time, then add the vanilla, lemon zest, and sour cream. In a seperate bowl, sift together the flour, baking powder, baking soda and salt. With the mixer on low speed, add the flour mixture to the batter until just combined. Fold in the blueberries and stir with a spatula to be sure the batter is completely mixed.
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