Evening Garlic Soup in the Manner of the Corrèze from The Cooking of South West France by Paula Wolf

Ingredients

• 2½ tablespoons rendered duck fat or 3 tablespoons unsalted butter
• 1 tablespoon all-purpose flour
• 2 eggs, separated
• ¼ cup thinly sliced garlic
• 2 medium onions, finely chopped
• 4 teaspoons red wine vinegar
• 4½ cups poultry or meat stock, degreased and heated to lukewarm
• Salt and freshly ground pepper to taste