BUTTERMILK SALAD DRESSING

I got this one from my aunt! She let me scan her newest Taste of Home book - made this tonight and it is quite yummy . . . hoping it will thicken up a bit in the fridge, though. It seemed awfully watered down.  It tasted WONDERFUL on our salads!!!

INGREDIENTS:
2 C buttermilk (I used the substitution of 1 Tbl white vinegar + enough milk to make 1 C = 1 C of buttermilk)
2 C mayo
1 Tbl onion powder
1 Tbl parsley
1-1/2 tsp garlic powder
1/2 tsp salt
1/2 tsp celery salt
1/4 tsp pepper

DIRECTIONS:
Whisk all ingredients until smooth. Store in refrigerator.