Peel and dice the onion and garlic. Heat the butter over medium heat and sweat the onion and garlic cubes well. Deglaze with the white wine and then pour the broth and cream on top. Bring the soup to the boil and then stir in the grated Parmesan and mustard. Then froth the soup with a hand blender. Then bring to the boil again and season with salt and pepper.
Divide between 4 plates and garnish with a teaspoon of pesto each. You can also serve croutons.