Heat oven to 350°F. Coat 6-cup soufflé dish with cooking spray.
Melt butter in saucepan. Stir in flour, salt and pepper; cook, stirring, 1 minute until blended. Stir in milk until smooth; cook, stirring, until sauce thickens and bubbles, about 1 minute. Remove from heat. Stir in cheese until melted. Stir in chives. Transfer to large bowl; cool.
Beat egg yolks in small bowl until thick. Fold into cheese mixture.
Beat whites with cream of tartar in large bowl until soft peaks form. Stir one-quarter of whites into sauce; fold in remaining whites. Pour into prepared dish.
For top-hat effect, run tip of teaspoon in groove around soufflé mixture, 1-1/4 inches from dish edge.
Bake in 350°F oven 45 minutes, until puffed and golden brown.
