Cook sausage and onion in a large skillet over medium heat, stirring until sausage crumbles and is no longer pink; drain well.
Return mixture to skillet; add 1 cup Cheddar cheese, cream cheese, and marjoram, stirring until cheeses melt.
Spoon 3 tablespoons filling down center of each crêpe.
Roll up and place, seam sides down, in a lightly greased 13- x 9-inch baking dish.
Bake, covered, at 350° for 15 minutes.
Stir together sour cream and butter; spoon over crêpes.
Bake 5 more minutes.
Sprinkle with remaining 1 cup Cheddar cheese and parsley.
