Butter inside and edge of 2-quart souffle dish.
Sprinkle with 1 tablespoon sugar.
Place collar of buttered waxed paper around dish and tie with string.
Slice 4 oranges; set slices aside.
Juice 2 oranges with lemon and strain to obtain 3/4 juice (additional juice may be needed).
Set aside.
Combine minced orange peel, 7 tablespoons sugar and apricots in processor or blender in batches.
Mix thoroughly.
Place mixture in saucepan with juice and butter.
Heat until butter is melted.
Blend 6 egg yolks until light in processor or with electric mixer.
With machine still running, pour hot juice mixture in very slowly.
Mixture can be prepared ahead to this point.
Cover and let stand at room temperature.
Place rack in middle of oven.
Preheat oven to 425°F.
Beat egg whites until foamy.
Add cream of tartar and salt and beat until stiff but not dry.
Gently fold in remaining 1/4 cup sugar.
Fold 1/4 of very warm orange mixture (reheated if prepared in advance) into egg whites.
Carefully fold egg whites into remaining mixture.
Place in prepared dish using spatula.
Bake until souffle is puffed and very brown, 16 to 17 minutes.