Melt butter in heavy 3 quart cast-iron pan over low heat. Add onions and cook, covered, for 15 minutes. Uncover and continue cooking 30-40 minutes, stirring frequently, or until onion turn deep golden color. Add stock and nutmeg. Cover and bring to boil. Reduce heat and simmer 15 minutes. Bring beer to boil in small pan over medium heat. Boil until reduced by half. Remove from heat and add cheese, stirring until melted. Transfer mixture to blender. Add one cup onion soup and blend until smooth. Reserve. Remove onion mixture from heat and strain, reserving liquid. Transfer onions to blender or food processor and puree until very smooth. Return puree to pan. Add reserved liquid and cheese mixture. Add salt and season to taste with pepper. Serve very hot in tureen. Makes 5 servings. Source: Lon Halls "Cooking With Beer" from CompuServe.