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1
Preheat the oven to 375 degrees F. Line one 12-cup standard muffin tin with cupcake liners.
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2
Sift together the flour, baking powder and 3/4 teaspoon of the salt.
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3
Beat together the butter and 1 cup of the sugar with an electric mixer until pale and fluffy, about 5 minutes.
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4
Beat in the egg, yolk, zest and 1 1/2 teaspoons of the vanilla.
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5
Reduce the speed to low and add the flour mixture in three additions alternating with the milk, beginning and ending with the flour mixture.
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6
Divide the batter among the muffin cups and bake until a tester inserted in the middle of the cakes come out clean, 20 to 25 minutes.
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7
Cool the cakes for 10 minutes in the tin, and then remove and cool completely on a rack.
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8
Put the lemon curd in a piping bag fitted with a 1/8-inch-round pastry tip.
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9
Insert the tip into the center of each cupcake and pipe in equal amounts of curd.
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10
Combine the egg whites, corn syrup, the remaining 1/2 cup sugar, the remaining 1 teaspoon vanilla and the remaining pinch of salt in a metal bowl set over a saucepan of simmering water.
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11
Beat with an electric mixer until thick and fluffy, about 7 minutes.
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12
Remove from the heat and beat until the frosting is slightly cooled, about 2 minutes longer.
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13
Mound the frosting on top of the cupcakes.
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14
If desired, use a kitchen torch to brown the frosting and garnish with a lemon candy.
