In large bowl add ranch salad dressing mix to buttermilk. Mix well with wire whisk or electric mixer at low speed.
Add mayonnaise and continue mixing at low speed about 2 minutes until smooth.
Blend in diced jalapenos, caynenne pepper and shredded cheese until combined.
Refrigerate 3-4 hours so dressing will thicken. Stir before using. Keep refrigerated.
NOTE: If you desire a smoother consistency substitute cheddar cheese sauce that has cooled to room temperature for the shredded cheese.