Heat the butter and olive oil in a large saucepan over medium heat. Add the diced onion, leek and minced garlic and saute for 2-3 minutes or until softened.
Add the chopped carrots, celery, red capsicum and thyme and saute for a further 3 minutes.
Add the plain flour and mix to coat. Cook for 1 minute.
Add 1 cup of the chicken stock liquid and stir until the flour has dissolved into the broth.
Add the remaining chicken stock liquid, milk, cooked (shredded) chicken and corn kernels. Bring the soup to a low simmer and cook for 20 minutes.
Stir through the baby spinach, season with salt and pepper and serve with croutons.
Notes
Chicken - you can cook and then shred 200g of chicken breasts, thighs or tenderloins. Or to save time, use leftover cooked chicken or a store-bought BBQ chicken. Shred before using.