Cream of Broccoli and Cheddar soup

1 1/2 pounds broccoli trimmed
2 tablespoons unsalted butter
1 yellow onion, chopped
1/4 cup flour
5 Cups Chicken stock
1/2 teaspoon dried thyme
1 tablespoon lemon juice
2 cups milk
1/2 pound cheddar cheese

Directions:

1. coarsley chop broccoli and set aside
2. in a large saucepan, melt butter over medium heat. Add the onion and saute until it begins to brown 5-7 minutes. sprinkle in flour and saute, stirring for about 1 minute more. whisking, slowly pour in the stock. add the chopped broccoli, thyme, and lemon juice and bring to boil. reduce to low and cover, simmer until the broccoli is very tender about 20 m inutes.
3. in small batches, puree the soup in a food mil, return the puree to the pan and stir in milk and bring to a simmer over low heat
4. sprinkle the cheese into the soup, stir over low heat until cheese melts