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1
Butter the cake-pan bottom, cover it with a parchment circle, then butter and flour the entire inside of the pan.
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2
Arrange a rack in the center of the oven, and preheat to 350 .
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3
Sift together the corn flour, white flour, and potato starch.
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4
Sprinkle yeast over 1/4 cup warm water, and let it dissolve.
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5
In the bowl of the mixer, cream together the sugar and 7 ounces butter for several minutes on high speed, scraping down the bowl several times, until light and smooth.
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6
Beat in the egg yolks one at a time; scrape down the bowl, and fluff up the batter on high speed.
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7
Lower the speed, and incorporate the dry ingredients, alternating with the yeast water, in two or three additions.
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8
Mix only briefly after adding the flours, but scrape the bowl and beaters well, and fold the batter over with a rubber spatulait will be stiffto be sure the dry ingredients are evenly moistened.
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9
With the whisk attachment or a hand whisk, whip the egg whites in a clean bowl, with the 1/8 teaspoon salt, to firm peaks.
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10
Stir a third of the whites into the batter to lighten it, then gently fold in the remainder.
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11
Scrape the batter into the prepared pan, and spread it in an even layer.
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12
Bake for about 40 minutes, or until the top is golden brown and springs back to the touch, and the cake is starting to pull away from the sides of the pan.
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13
Let it cool on a wire rack for an hour, then remove from the pan and dust with powdered sugar if you wish.
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14
Cut the cake in wedges, and serve warm or at room temperature (or reheated in a low oven, if you like), plain or fancy.
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15
(Wrap well and freeze for a month or so; defrost at room temperature before removing the wrappings.)
