Beef and Blue Cocktail Sandwiches

Blue Cheese Spread:
1 1/2 (8 ounce) packages cream cheese, softened
8 ounces sour cream
2 teaspoons Worcestershire sauce
1 teaspoon hot sauce
6 ounces blue cheese, crumbled
1/2 cup walnut halves, toasted and chopped

Caramelized Onions:
3 tablespoons extra-virgin olive oil
3 large, sweet onions, thinly sliced
1 1/2 tablespoons balsamic vinegar
1/4 teaspoon fresh ground pepper, or to taste
36 cocktail sandwich buns
1 1/2 pounds deli sliced roast beef

Blue Cheese Spread: Beat cream cheese with an electric mixer until creamy. Add sour cream, Worcestershire sauce and hot sauce. Stir until blended. Stir in blue cheese and walnuts. Cover and chill for two hours.

Caramelized Onions: Heat oil in a Dutch oven over medium heat. Add onions. Cook, stirring often, 30 minutes or until caramelized.

Stir in vinegar and pepper. Remove from heat, cool slightly.

Assembly: Split rolls in half. Spread tops and bottoms of rolls with the blue cheese spread. Place roast beef on bottoms of rolls. Top beef with caramelized onions. Cover with tops.

NOTE: The blue cheese spread and caramelized onions may be made one day ahead. Assemble the sandwiches no more than 2 hours before serving.