1/4 cup Grand Marnier 4 tablespoons sugar, plus more if necessary
3 tablespoons tangerine juice
In a medium saucepan, heat orange juice and 1 cup sugar until sugar is dissolved. Add tangerines, and simmer, covered, until tangerines are very tender, 25 to 35 minutes. Strain through a fine sieve, pressing gently to extract most of the juice, reserving both fruit and juice.
In a food processor, combine tangerines and 1/2 cup tangerine juice. Puree until fairly coarse. Add Grand Marnier, and process to combine. The purée should just hold its shape without being sticky; if necessary, work in a little more juice. Transfer the purée to the saucepan.
Preheat the oven to 400 degrees. Generously butter six 8 ounce ramekins, chill them for 10 minutes in the freezer, and butter them again. Set on a baking sheet. In the bowl of an electric mixer fitted with the whisk attachment, whisk egg whites with a tablespoon of sugar until the whites hold a stiff peak, 1 to 2 minutes. Add remaining 1/2 cup sugar, stirring with a spoon until whites are glossy and hold a long peak when the spoon is lifted, about 1 minute. Heat the tangerine purée until just simmering. Remove from heat, and add about 1/4 of the whites, stirring until well mixed. Add this mixture to the remaining whites, lightly folding to combine.
Transfer soufflé mixture to ramekins, filling to the rim and mounding generously in the center. Run your thumb around the edge of the mixture to make it rise evenly. Bake the soufflés until puffed and brown, 10 to 12 minutes. Set the ramekins on small plates, preferably lined with a napkin to prevent slipping. Serve immediately with orange strawberry sauce.
ORANGE STRAWBERRY SAUCE
In a blender, purée strawberries, Grand Marnier, sugar, and tangerine juice. Taste, adding more sugar, if desired. Chill before serving.