1. With 2 tablespoons butter, coat inside of eight 1-cup souffle dishes. Place 2 tablespoons sugar into one dish, coating; shake excess into next dish; continue coating.
2. Heat oven to 375 degrees F. In saucepan, combine flour, 1/4 cup sugar, salt. Gradually whisk in milk. Over high heat, bring to boiling, whisking, until thickened and pulls away from side of pan, 3 minutes. Remove from heat. Stir in remaining 2 tablespoons butter, liqueur and rind. Whisk in yolks, one at a time, whisking 10 seconds after each. Scrape into bowl.
3. In large bowl, beat 7 whites and cream of tartar on high speed until soft peaks form. Gradually beat in remaining 1/4 cup sugar, 1 tablespoon at a time, until stiff peaks form.
4. Fold quarter of whites into yolk mixture. Fold in remaining whites. Spoon about 1 cup mixture into each dish. Run finger around top perimeter, an inch in from sides.
5. Bake at 375 degrees F until tops are browned and puffed, 20 to 25 minutes. Sprinkle with confectioners sugar, if desired.