Broccoli, Leek and Potato Soup

I have been seeing combinations of broccoli, leek, and potatoes in soups from a few magazines, but could not find one that suited my taste. So, I made one up. This was supposed to be a project in action, but it was loved by my husband and 13-year-old daughter, so I am calling it complete. Here it is:

Broccoli, Leek and Potato Soup

1 stick butter
2 heads broccoli, chopped
1 leek, white and light green parts, sliced and washed
3 medium potatoes, peeled and cubed
chicken or vegetable stock
1 sprig rosemary
salt and pepper

Melt butter in a stockpot. Add broccoli, leek, potato and saute until vegetables are coated with butter and starting to brown. They will begin to smell delicious. Add enough stock to cover the vegetables. Season with salt and pepper and place rosemary sprig on top. Simmer until vegetables are tender. Remove rosemary and blend soup with an immersion blender. Serve.