Big Bob Gibson Mustard Slaw

Why I Love This Recipe
I LUV, Luv slaw! I found this from Martha Stewart Living. This is a little bit different from what I usually fix.
(Be sure to SHRED!)
Ingredients You'll Need
2 med. heads green cabbage,(about 4 lbs. ea.,) cored and *shredded.
1 lg. white onion, *shredded
1 grn.bell pepper. seeded, deveined, and *shredded
1 lg. carrot, peeled and *shredded
1 lg. rib celery, *shredded
Combine and mix in a large bowl above ingred.
DRESSING:
In a small saucepan, combine:
3/4 c. apple cider vinegar
3/4 c. yellow mustard
1/2 c. ketchup
1/2 c. sour cream
1/4 c. mayonnaise
1 tbsp salt (coarse)
1/2 tsp. cayenne pepper
Directions
Bring to a boil, whisking frequently. Pour over cabbage mixture.
ADD 1 1/4 cups sugar (or to taste,) and stir to combine. COVER with plastic wrap and CHILL.