Preheat two tablespoons of vegetable oil and saute the onions until they turn golden brown. Add in the flour and stir well until the ingredients combine. Add the stock and simmer for 15 minutes while stirring. Season with salt and pepper, stir well and turn off the heat.
Pour the soup into oven safe bowls, place a slice of baguette into each bowl, sprinkle some Gruyere cheese on top. Place the bowls into a preheated oven until the cheese is melted. Garnish with parsley and serve hot.