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1
Preheat the oven to 350.
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2
Butter and flour a 9-inch round cake pan.
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3
Toast the hazelnuts on a rimmed baking sheet, stirring occasionally, for about 10 minutes, or until lightly browned.
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4
Let the hazelnuts cool on the baking sheets, then transfer them to a kitchen towel and rub them together to remove the skins.
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5
Transfer the hazelnuts to a food processor and finely chop.
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6
In a small bowl, sift the flour with the baking powder and salt.
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7
In a large bowl, using a handheld mixer, beat the butter with the granulated sugar until fluffy.
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8
Beat in the eggs, 1 at a time, until incorporated.
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9
Using a rubber spatula, fold in the flour mixture in 3 batches, alternating with the rum and hazelnuts.
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10
In a medium stainless steel bowl, beat the egg whites until stiff.
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11
Beat one-third of the egg whites into the batter, then gently fold in the remaining whites.
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12
Scrape the batter into the prepared pan and bake for about 35 minutes, or until the cake springs back when lightly pressed.
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13
Transfer to a rack and let cool in the pan for 15 minutes.
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14
Turn the cake out onto the rack and cover loosely with a kitchen towel until cooled to room temperature.
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15
Turn the cake right side up and dust the top with confectioners' sugar, then cut into wedges and serve.
