Heat butter and oil in a large saucepan and saute the vegetables for a few minutes or until softened. Coat the sautéed vegetables in plain flour and allowing it to cook for 1 minute before slowly adding the liquid.
Add cooked chicken, liquid chicken stock, milk and corn kernels and cook over a low heat for 20 minutes. Stir through the baby spinach, season with salt and pepper and serve with crunchy croutons.