1- in a large pot melt butter over medium heat. Add potatoes and onion, cook, stirring until onion is tender-- about 8 minutes.
2- Add flour and cook 2 more minutes
3- Gradually stir in chicken broth and milk. Bring to a simmer and cook until potatoes are nearly tender-- about 5 minutes longer. Add broccoli and cook until tender about 5 more minutes.
4- Remove from heat and stir in cheese and lemon juice and season.