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1
Preheat the oven to 375F.
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2
With a pastry brush, butter the bottom and sides of an 8-inch springform cake pan.
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3
With a whisk or electric beater, beat the egg yolks for about 1 minute, then slowly pour in the sugar.
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4
Continue beating until the mixture falls back on itself in a ribbon when the beater is lifted out of the bowl.
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5
Beat in the grated lemon rind and lemon juice, and with a rubber spatula, fold in the hazelnuts.
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6
In another bowl, and with a clean beater, beat the egg whites until they form stiff peaks on the beater when it is lifted out of the bowl.
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7
Gently but thoroughly fold the whites into the egg-yolk mixture until no streaks of white show.
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8
Pour the batter into the buttered pan and spread evenly to the sides with the spatula.
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9
Bake in the center of the oven for about 40 minutes, or until it has puffed and has begun to come slightly away from the sides of the pan.
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10
Turn off heat and let cake rest in the oven for 15 minutes.
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11
Remove the sides of the pan and turn cake out on a cake rack.
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12
Cool to room temperature.
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13
To make the topping, beat the cream with a whisk or electric beater until it forms soft peaks.
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14
Then gradually beat in the rum and sugar and continue to beat until stiff.
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15
With a spatula, spread over the top of the cake and serve at once.
