Melt the butter in a saucepan and add 1 tablespoon of olive oil. Stir in the diced mushrooms and courgettes; cook gently over medium heat for 5 minutes, or until they are slightly softened and golden in colour.
Pour in the water and add the stock cubes.
Bring to the boil; reduce heat and simmer for 5 minutes.
Remove from heat. Use a hand held immersion blender to puree the soup. Season to taste with salt and freshly ground black pepper.
Season to taste with salt and freshly ground black. Add a splash of cream for a richer finish.