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1
Preheat the oven to 350 F degrees.
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2
Butter an 8x12 inch baking sheet, then line with buttered parchment paper, and set it aside.
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3
To make the sponge cake, place the eggs, sugar, lemon rind, and vanilla in the bowl of an electric mixer and beat at high speed until the mixture is light and has tripled in volume. Mix the flour with the baking powder. Using a rubber spatula, fold this in, being careful not to deflate the egg mixture too much.
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4
Pour the batter onto the prepared baking sheet with a 1-inch rim.
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5
Bake for 18-20 minutes, or until the sponge cake is very lightly browned. Let cool for 5 minutes.
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6
Then invert the cake onto a damp kitchen towel sprinkled with the confectioners' sugar. Gently peel off the parchment paper. Carefully roll the cake lengthwise in the towel. Wrap in foil and let cool at room temperature.
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7
To make the filling, whisk together the eggs, egg yolks, sugar, lemon rind and juice in a tempered glass bowl, then add the butter and place over a pot of simmering water. Cook over low heat whisking constantly until the lemon curd starts to thicken. This could take 20-30 minutes. Let cool at least an hour.
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8
Unroll the cake. Cover with the lemon curd, then carefully roll the cake again, this time without the towel. Transfer to a serving platter. Dust with confectioners' sugar. Chill 1 hour or longer.
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9
Slice and serve with fresh berries and whipped cream if desired.
