In a blender or food processor (or grate onion and beat with other ingredients) :

1 sm. onion, cut up
1 c. mayonnaise
1/3 c. oil
1/4 c. catsup
2 tbsp. sugar
2 tbsp. vinegar
1 tsp. prepared mustard
1/2 tsp. salt, paprika, and celery seed

Add after mixing: 1 cup (4 oz.) crumbled blue cheese.