Cut the oranges in half crosswise and squeeze out the juice. Strain and measure. You should have about 1 3/4 cups juice. Add more juice if you have less than this amount and remove juice if you have more.
Carefully scrape out and discard the pulp from the 2 navel oranges to form half shells. Combine 1/4 cup of the juice and the gelatin in a small saucepan. Set aside for 5 minutes to dissolve the gelatin. Heat the mixture slowly over low heat and stir constantly until smooth 3 to 4 minutes. Whisk in the remaining juice. Arrange the orange shells cut side up in muffin tins or ramekins. Divide the mixture among the 4 shells and cover each with plastic wrap. Chill until firm, at least 4 hours and preferably overnight. Cut each half into 3 wedges before serving.
Recipe courtesy of Sara Moulton, Sara Cooks at Home, Broadway Books, 2002