Slice the onions into rings. In a pot, melt a pat of butter and sauté the onions for 5 minutes until golden.

Meanwhile, prepare the broth by dissolving the chicken bouillon cube in 2 cups of water (about 500 ml). Add the white wine and broth to the pot. Season lightly with salt and pepper. Cover and simmer for 20 minutes. Preheat your oven to 350°F (180°C).

(Do this step during the last 10 minutes of the soup cooking) Place the bread rolls, sliced in half, on a sheet of parchment paper. Top the slices with Gruyère cheese. Bake for 10 minutes.

Place the bread slices on top of the soup before serving.