1. Heat oven to 250 degrees, with a rack in the center. Generously butter the wells of an egg-cake pan, and dust the wells with flour; tap out any excess. Set pan aside.

2. 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 vanilla and lemon zest; beat to combine. Add the eggs, one at a time, mixing well after each addition and scraping down sides of bowl.

3. Sift together the flour, baking powder, and salt. Add to butter mixture. Beat until just combined. Spoon batter into each of 6 wells in the cake pan, filling to within 1/2 inch of the rim. (If you are using an egg-cake pan with more than 6 wells, alternate between the filled and empty ones.)

4. Bake the egg cakes for 10 minutes. Increase the oven temperature to 350 degrees, and bake until the cakes are golden, 10 to 12 minutes more. Transfer egg-cake pan to a wire rack, and let cool slightly. While the cakes are baking make the first batch of glaze.

5. 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 3 cakes, completely coating the outside of the cake. Make second batch of glaze, and glaze remaining 3 cakes. Let glaze set completely, about 1 hour.

6. 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 wire rack.

7. Place cakes glazed-side down on the clean wire rack; generously dust flat side with confectioners' sugar. Fit a pastry bag with a coupler, and fill the bag with lemon curd. (Alternately, the curd can be carefully spooned into the hole.) Fill each hole with lemon curd until it resembles a slightly rounded egg yolk.

8. In a large bowl, combine fruit and Grand Marnier, and toss to coat. On each dessert plate, make a nest of fruit, and place a decorated cake in the center. Garnish with mint leaves, and serve.