I copied and customized this recipe from rezept/zwiebelsuppe
Traditional French onion soups often rely heavily on dark, heavily caramelized alliums and robust red wine reductions. This European variant takes a lighter path. Slicing seventy-five grams of onions into clean half-rings sets the stage for a completely different flavor profile. Butter provides the fat for the initial stewing phase. Controlling the heat determines ultimate success here. Keep the burner on low to render the onions translucent without browning them. High heat introduces bitter scorched notes that ruin the base.
Substitutions alter the final character significantly. Swapping the specified white wine for a dry vermouth adds herbal complexity, though a crisp Sauvignon Blanc preserves the intended acidity. If beef broth is unavailable, a rich vegetable stock works, but it demands an extra pinch of salt to match the savory depth of beef. When adding the liquids, pour in the wine first and let it reduce partially before introducing the broth. Simmer the combined mixture for thirty minutes to meld the flavors completely.
Dairy adjustments require careful consideration for the topping. Standard Gruyère provides the classic melt, but aged Emmental or sharp white cheddar function as viable alternatives if grated finely. Toast the bread hard before submerging it to prevent immediate disintegration under the hot broth. Garlic powder seasons the soup efficiently at the end, dispersing evenly without leaving raw granular pockets behind.