Tangerine Soufflé with Citrus Coulis

Name: Tangerine Soufflé with Citrus Coulis
Ingredients: 6 tangerines, peeled; 1/4 cup fresh tangerine juice; 3 tablespoons sugar; 1 tablespoon (or more) fresh lemon juice; Unsalted butter (for dish); 5 tablespoons plus 1/2 cup sugar, divided; 3/4 cup fresh tangerine juice, divided; 1 tablespoon plus 2 teaspoons cornstarch; 2 teaspoons finely grated tangerine zest; 1 teaspoon fresh lemon juice; 6 large egg whites, room temperature; 1/4 teaspoon cream of tartar; 4 large egg yolks, room temperature; Powdered sugar; A 2-quart soufflé dish