Preheat oven to 400°. Lightly coat 5 lightly greased 4-oz. ramekins with granulated sugar, shaking out excess. Place on a jelly-roll pan.
Whisk together 1 cup lemon curd and next 2 ingredients in a large bowl.
Beat egg whites with cream of tartar at medium speed with an electric mixer 1 to 2 minutes or until soft peaks form. Gently fold one-fourth of egg white mixture into curd mixture using a rubber spatula; fold in remaining egg whites just until blended. Pour gently into ramekins, filling to top. Run tip of thumb around edges of ramekins, wiping clean.
Bake at 400° for 10 minutes; reduce heat to 350°, and bake 4 minutes or until soufflés rise and are set. (Center should be slightly loose when shaken.) Dust with powdered sugar. Serve immediately with remaining lemon curd.