1 1/2 pounds (680 grams or 24 ounces or about 5 cups) thinly sliced yellow onions
3 tablespoons (42 grams or 1 1/2 ounces) unsalted butter
1 tablespoon (15 ml) olive oil
1 teaspoon (5 grams) table salt, plus additional to taste
1/4 teaspoon (1 gram) granulated sugar (helps the onions to brown)
3 tablespoons (24 grams or 7/8 ounce) all-purpose flour
2 quarts (8 cups or 1.9 liters) beef or other brown stock*
1/2 cup (118 ml) dry white wine or dry white vermouth
Freshly ground black pepper
3 tablespoons (45 ml) cognac or brandy (optional)

To finish [Gratinée] (Optional)
1 tablespoon grated raw onion
1 to 2 cups (to taste) grated Swiss (I often use Gruyere) or a mixture of Swiss and Parmesan cheese
1 tablespoon butter, melted
12 to 16 1-inch thick rounds French bread, toasted until hard