Melt the butter in a large pot over medium heat. Add the broccoli stems, onions, dry mustard and some salt and pepper and saute until the onions are translucent, about 5 minutes. Deglaze with the sherry and then add the broccoli florets. Add the stock and simmer for 5 minutes. Carefully ladle everything into a blender along with the fresh spinach, Cheddar, cream and hot sauce and process until smooth, about 1 minute. Adjust with salt and pepper if necessary and adjust the thickness with more cream if necessary. Top with croutons and serve.
P.S. I always use store-bought croutons but I forgot to get croutons so we diced some French bread in cubes, sprinkled with olive oi, salt and pepper and toasted in the oven for 15 minutes at 400 and we got the croutons you see in my photos! They were delish!