Yummy Beer Cheese Dip

¼ c. butter ½ c. finely chopped onion ¼ c. flour 1 (12-oz.) can IPA beer ¼ c. half and half 6 oz. shredded fontina cheese 6 oz. shredded sharp cheddar cheese 1 T. Dijon mustard 1 t. Worcestershire sauce…