Cook pasta in salted water according to package directions.
In a large skillet, on low heat melt butter.
Whisk in flour, keeping the butter and flour moving.
Add minced onion and cook for 2-3 minutes or until onions are translucent.
Add chicken broth and milk, continue to whisk. Raise heat to medium-high, while whisking frequently, bring sauce to a boil. After 10-12 minutes, sauce will start to thicken. Add salt and pepper and remove from heat.