Combine first 4 ingredients, beating with a wire whisk until smooth. Add egg and beat well; stir in 2 teaspoons oil. Chill batter at least 2 hours.
Coat bottom of a 6" crêpe pan or heavy skillet with oil; place over medium heat until hot.
Pour 2 tablespoons batter into pan; quickly tilt pan in all directions so batter covers bottom of pan. Cook 1 minute or until crêpe can be shaken loose from pan. Turn crêpe over and cook about 30 seconds. Place crêpe on a dish towel to cool. Repeat with remaining batter. Stack crêpes between sheets of wax paper to prevent sticking.
Unwrap and chop 1 package of chocolate mint candies. Beat 2 1/2 cups whipping cream and powdered sugar at high speed of an electric mixer until stiff peaks form. Gently fold in chopped mint candies. Cover and freeze 5 minutes.
Spoon 1/3 cup whipped cream mixture in center of each crêpe. Fold left and right side of each crêpe toward center. Place, seam side down, in a dish and freeze at least 2 hours.
Combine remaining chocolate mint candies, 1/4 cup whipping cream, and corn syrup in a saucepan. Cook over medium-low heat until chocolate melts, stirring often. Remove from heat; let cool slightly.
Place 2 crêpes on each serving plate. Drizzle warm sauce over crêpes. Garnish, if desired.