1. Preheat oven to 225 degrees. Cut oranges into segments. Toss with 3 tablespoons liqueur; refrigerate.

2. Make meringue: Put egg whites, 1 cup sugar, and a pinch of salt in the heatproof bowl of an electric mixer. Set over a pan of simmering water; whisk constantly until sugar is melted and mixture is hot.

3. Fit mixer with whisk attachment; beat egg-white mixture on medium speed until soft peaks form. Raise speed to high; beat until cool, and stiff, glossy peaks form. Beat in vinegar and vanilla.

4. Using a rubber spatula, mound meringue into twelve 3-inch-wide rounds on parchment-paper-lined baking sheets. Swirl edges and make a well in center of each meringue. Bake until crisp and just set in center, 40 to 50 minutes. Let cool on sheet on a wire rack. When meringues are cool enough to handle, peel off parchment. Let cool completely.

5. Make custard: Stir together yolks, juice, remaining 1/4 cup each sugar and liqueur, and 1/8 teaspoon salt in a large heatproof bowl set over a pan of simmering water; whisk until thickened and a spoon leaves a wake, about 4 minutes. Pass mixture through a fine sieve into a bowl. Refrigerate until cold, about 1 hour.

6. Beat cream to soft peaks; fold into custard. Refrigerate until ready to serve, up to 4 hours (rewhisk before using).

7. Just before serving, mound custard in each meringue. Top custard mounds with orange segments and their juices.