I start by melting butter in a large soup pot. Once it’s hot, I toss in diced onion and cook until golden and soft. This step gives the soup a deep, savory flavor that sets the tone for the rest of the dish.
Next, I sprinkle the flour over the onions and stir until it coats evenly. Slowly, I whisk in the milk, cream, and chicken broth, making sure no lumps remain. After a few minutes of simmering, the soup thickens into a velvety, creamy base.
Once the base is ready, I stir in the shredded chicken, diced ham, and mustard. Then comes the best part — adding freshly grated Swiss cheese. It melts beautifully, giving the soup its rich, cordon bleu flavor.
Finally, I taste the soup and adjust the seasoning with salt and pepper. Right before serving, I sprinkle fresh parsley on top. I like serving it piping hot with crunchy croutons or a slice of warm, toasted bread.