Spray bottom and side of 9-inch springform pan with cooking spray; dust side with 2 tsp. sugar.
Microwave chocolate and butter in large microwaveable bowl on HIGH 1-1/2 min. or until both are completely melted, stirring every 30 sec. Stir in remaining sugar and mint.
Beat eggs in medium bowl with mixer on high speed 9 to 10 min. or thickened and quadrupled in volume. Add half the eggs to chocolate mixture; stir gently until blended. Repeat with remaining eggs. Pour into prepared pan.
Bake 35 min. or until toothpick inserted in center comes out with fudgy crumbs. (Do not overbake.) Cool 10 min. Run small knife around rim of pan to loosen cake; remove rim. Cool cake completely.