2 lg. Spanish onions (1 lb. total)
6 oz. bleu cheese, broken into halved pieces
6 tbsp. (3/4 stick) unsalted butter, room temperature
2 tsp. Worcestershire sauce
1/2 tsp. dried dill weed
Freshly ground pepper

Generously butter 9x13 baking dish. Position rack in center of oven and preheat to 425 degrees.

Medium slicer: Place onions in feed tube and slice using firm pressure. Transfer to prepared dish, spreading evenly.

Steel knife: Combine remaining ingredients in work bowl and mix 8 seconds, stopping machine once to scrape down sides of bowl. Spread cheese mixture over onions using flexible spatula. Bake 20 minutes; broil briefly until top is brown and bubbly. Serve hot.