Hot Gruyere Spinach Dip

2 tablespoons butter
1 medium onion, finely chopped (about 1/2 cup)
2 (10 ounce) packages frozen creamed spinach, thawed
1 cup half-and-half
8 ounces gruyere cheese, shredded (2 cups)
1 tablespoon dry sherry (optional)
breadsticks (optional) or French bread, slices (optional)

Melt butter in medium saucepan over medium heat.
Add onions; cook and stir for 5 minutes, or until tender.
Add creamed spinach and half-and-half; cook and stir 5 minutes, or until hot.
Stir in cheese and (if desired) the dry sherry.
Cook 2 minutes, or until cheese is melted.
Serve with breadsticks or French bread slices, if desired.
NOTE: Dip may be held in a small slow cooker over low heat for several hours.