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1
Cake: position oven rack in middle position; preheat to 325u00b0.
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2
Grease and flour a 13 x 9 inch baking pan.
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3
In a bowl, combine the flour, baking powder, baking soda, and salt.
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4
In a liquid measuring cup, combine the buttermilk, lemon juice, and vanilla.
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5
In a big bowl, beat together the sugar and lemon zest with an electric mixer on medium speed, until moist and fragrant, about 1 minute.
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6
Transfer 1/4 cup of sugar mixture to a small bowl, cover, and reserve.
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7
Add the butter to the remaining sugar mixture and beat until light and fluffy, about 2 minutes.
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8
Beat in the eggs, one at a time, and the yolk until combined.
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9
Decrease mixer speed to low.
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10
Mix in 1/3 of the flour mixture, followed by half of the buttermilk mixture.
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11
Repeat with half the remaining flour mixture and the remaining buttermilk mixture.
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12
Add the remaining flour mixture and mix until smooth, about 30 seconds.
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13
Give the batter a final stir with a rubber spatula to make sure it is thoroughly combined.
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14
Scrape the batter into the prepared pan, smooth the top, and gently tap the pan on the work surface to settle the batter.
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15
Bake until the cake is golden brown and a pick comes out clean, about 28-34 minutes, rotating the pan halfway through baking.
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16
Transfer pan to a wire rack and let the cake cool for 10 minutes.
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17
Glaze: meanwhile, whisk the glaze ingredients together until smooth.
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18
Gently spread the glaze over the warm cake and sprinkle evenly with the reserved sugar mixture.
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19
Cool completely, at least 2 hours, then serve.
