Preheat oven to 250 degrees F. Generously butter the wells of an egg-cake pan, and dust the wells with flour; tap out any excess flour. Set pan aside. In the bowl of an electric mixer fitted with the whisk attachment, combine butter and granulated sugar. Beat on medium speed until light and fluffy, about 2 minutes. Add the seeds from the vanilla bean and the lemon zest; beat to combine. Add eggs, 1 at a time, mixing well after each addition and scraping sides of bowl. Into a medium bowl, sift together flour, baking powder, and salt. Add to butter mixture. Beat until just combined. Spoon batter into each of nine wells, filling them about half full. Bake the egg cakes for 10 minutes. Raise the oven temperature to 350 degrees F, and bake until the cakes are golden, 10 to 12 minutes more. Transfer egg-cake pan to a wire rack, and let cool slightly, about 10 minutes. Invert pan, and remove cakes. Using a serrated knife, trim the cakes to resemble eggs sliced in half. (To make trimming easier, place the eggs in resealable plastic bags, and transfer to freezer for 45 minutes.) Using a melon baller, scoop out a 1-inch-diameter hole in each cake. Set a wire rack over a baking sheet. Place the cakes flat-side down on the wire rack. Working quickly, pour the colored butter glaze over each cake, completely coating the outside. After about 1 minute, gently lift the cakes with a wooden skewer so that they don't stick to the wire rack. Let the glaze set completely, about 1 hour. Turn the glazed cakes over, and trim away any excess glaze with a paring knife, so glaze is flush with the flat side of cake. Wash and dry the wire rack. Place cakes glazed side down on the wire rack; generously dust flat side with confectioners' sugar. Fit a pastry bag with a #11 pastry tip, and fill the bag with lemon curd. Fill each hole with lemon curd until the "yolk" appears slightly rounded. On each dessert plate, place a decorated cake. Garnish each serving with a mint sprig.
Place milk in a small bowl, and stir in liquid paste color until desired color is achieved; set aside. Place confectioners' sugar in a medium bowl, and set aside. In a small saucepan, melt butter over medium heat. Remove from heat, and immediately pour butter into the bowl with the sugar. Add half of the milk, and whisk until smooth. Add the remaining milk as needed to make a mixture that is just thin enough so that it runs down the sides of the cakes. Yield: Glaze for 9 egg cakes
Place egg yolks, lemon zest, lemon juice, and sugar in a small saucepan; whisk to combine. Set over medium heat, and stir constantly with a wooden spoon, making sure to stir sides and bottom of pan. Cook until mixture is thick enough to coat back of wooden spoon, 5 to 7 minutes. Remove saucepan from heat. Add butter, 1 piece at a time, stirring with the wooden spoon until consistency is smooth. Transfer mixture to a medium bowl. Lay a sheet of plastic wrap directly on the surface of the curd to prevent a skin from forming; wrap tightly. Let cool; refrigerate until firm and chilled, at least 1 hour. Store refrigerated in an airtight container for up to 2 days. Yield: 1 1/2 cups
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