French Onion Grilled Cheese

3 T butter, plus more butter for bread
2 med onions, thinly sliced
Salt and pepper
3 T chicken broth
4 slices sourdough bread
1 C Gruyere cheese, grated

In large, deep skillet, melt butter over medium heat. Add onions; cook and stir until softened, 3-4 minutes. Season with salt and pepper; cover. Cook, stirring occasionally, until golden brown, about 25 min. Stir in broth, scraping up browned bits from bottom of pan. Cook 1 min and remove from heat. Spread each side of bread with butter. Assemble sandwiches on skillet: bread, cheese, onions, cheese, bread. Cook on each side until golden brown and cheese is melted.