Grilled Muenster with Carmelized Onion Sandwiches

In skillet on med-high heat:

melt 3 T. butter or margarine

Add:
1 medium onion which has been sliced and separated into rings
Cook until tender, reduce heat to low, add:
1 t. brown sugar
Cook 20-25 minutes, stirring occasionally, until onion is golden and glazed; set aside.

while onion is cooking,

spread mustard on 8 slices pumpernickel rye bread

top 4 of these with muenster chese

spoon caramelized onions onto cheese, top with another slice of pumpernickel

spread butter/margarine on top and bottom of sandwich, place in skillet on med-low, cooking until cheese is melted