Line 8-inch square baking pan with foil, folding excess foil over sides of pan to use as handles.
Combine sugar, marshmallow creme, milk, butter and salt in large saucepan; heat over medium heat until marshmallow creme is melted, stirring occasionally. Increase heat to medium-high. Bring to a fast boil; boil 5 minutes or until temperature reaches 212˚F., stirring constantly. Remove from heat.
Stir in semisweet and milk chocolate until melted. Stir in lemon oil. Pour into pan. Refrigerate overnight or until firm. Cut into squares.
*Not extract – you must use lemon oil.
If unable to find you can substitute 1/4 cup lemon juice, 1 tablespoon grated lemon peel and 1 teaspoon lemon extract.