Hot Roast Beef Sandwiches with Horseradish Cream

• 1 pound thickly sliced deli roast beef
• 4 slices bread
• 2 tablespoons butter

For the Onion Gravy:

• 1 large onion or 2 medium, thinly sliced
• 1 tablespoon olive oil
• 1 tablespoon butter
• salt and pepper to taste
• 2 tablespoons parsley roughly chopped
• 2 tablespoons all-purpose flour
• 1 ½ cups beef broth or stock

For the Horseradish Cream:

• ½ cup sour cream
• 2 teaspoons prepared horseradish
• ½ teaspoon dried dill weed
• salt and pepper to taste