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1
Position oven rack in lower third of oven; preheat to 350; butter a 13x9 inch baking pan.
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2
Using a triple sifter, sift together the flour, baking powder, and salt; set aside.
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3
Cut the butter into 1-inch pieces and place in the large bowl of a stand mixer with paddle attachment.
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4
Add in the lemon and orange rinds and soften on low speed.
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5
Increase to med-high and cream until smooth and light in color, about 1 1/2-2 minutes.
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6
Add the sugar 1 tablespoon at a time, taking about 6-8 minutes to blend it in well.
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7
Scrape the sides of the bowl occasionally.
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8
Add in eggs, 1 at a time at 1-minute intervals, scraping down the sides of the bowl as needed.
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9
Decrease speed to low; in a small bowl, combine the water, lemon juice, and orange juice.
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10
Add the dry ingredients alternating with the liquids, dividing the flour mixture into 3 parts and the liquid into two parts, starting and ending with the flour.
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11
Mix just until incorporated after each addition; do not worry if the batter appears to curdle, it should smooth out after the flour is blended inches.
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12
Scrape the sides of the bowl and mix for 10 seconds longer.
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13
Spoon batter into prepared pan, smoothing with the back of a spoon.
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14
Center the pan on the oven rack and bake for 30-35 minutes, or until the cake is golden brown on top, springy to touch, and begins to come away from the sides of the pan.
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15
Remove pan from oven and set on a cake rack to cool.
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16
Just before serving, place powdered sugar in a fine mesh strainer and dust the top of the cake; cut into squares and serve.
