Grate zest (colored portion of citrus peel with no membrane€”use light touch when grating) of 1 tangerine and chop very fine.
Place in small saucepan over low heat with 1 tablespoon Grand Marnier; heat until liqueur has evaporated.
Cut off top third of 7 remaining tangerines (halve if using oranges).
Remove flesh carefully, leaving shells intact for filling.
Push pulp through fine strainer, reserving juice.
Set aside 6 shells.
Beat egg yolks with 2 1/2 tablespoons sugar in medium bowl until mixture thickens and is very pale in color.
Stir in flour.
Gradually add warm milk.
Transfer mixture to a heavy-bottomed small pan; place over low heat and whisk until custard thickens, approximately 10 minutes.
Gradually add 1/2 cup tangerine juice and continue to whisk until custard thickens again.
Remove from heat and force through fine strainer.
Cool before adding remaining 1 tablespoon Grand Marnier and lemon juice.
Drain mandarin sections; cut into small pieces.
Combine with 2/3 of the strained custard.
Add tangerine zest.
Spoon into reserved tangerine shells, dividing equally.
Preheat oven to 325°F.
Beat egg whites until soft peaks form.
Add remaining 1/2 tablespoon sugar and continue beating until quite stiff.
Fold in reserved custard.
Place in pastry bag fitted with 1/3-inch star tube.
Pipe meringue into tangerine shells, mounding it in circular fashion.
Arrange tangerines in shallow baking dish with 1/2 cup water.
Bake until lightly browned, about 20 minutes.