Cream of Broccoli Soup

My sister-in-law made this soup for us last summer, and we loved it. Yummy! I love it with breadsticks.
Some great tips from my sister-in-law for this soup are: "We LOVE this soup and make it whenever broccoli is on sale. It's easy to half, and the proportions don't have to be exact. Often we do it without celery, and I always saute chopped up broccoli stems with the onions. And red onions are the best for this soup. The cream mixture always takes longer than you think it should, but it usually comes 'round. Here's the original link."

Cream of Broccoli SoupIngredients
2 tablespoons butter
1 onion, chopped
1 stalk celery, chopped
3 cups chicken broth
8 cups broccoli florets
3 tablespoons butter
3 tablespoons all-purpose flour
2 cups milk
ground black pepper to taste

Directions
1.Melt 2 tablespoons butter in medium sized stock pot, and saute onion and celery until tender. Add broccoli and broth, cover and simmer for 10 minutes.
2.Pour the soup into a blender, filling the pitcher no more than halfway full. Hold down the lid of the blender with a folded kitchen towel, and carefully start the blender, using a few quick pulses to get the soup moving before leaving it on to puree. Puree in batches until smooth and pour into a clean pot. Alternately, you can use a stick blender and puree the soup right in the cooking pot.
3.In small saucepan, over medium-heat melt 3 tablespoons butter, stir in flour and add milk. Stir until thick and bubbly, and add to soup. Season with pepper and serve.