I was on a diet once (well, I tried anyway) and I used to fill my days -- and stomach -- with a lot of fresh vegetables. I love fresh vegetables of course, but sometimes I just craved something naughty too, so I made a buttermilk blue cheese dressing that was only about 50 calories for 1/4 cup! And it was great. I put it on my veggies, but also my grilled meats and I even dipped those nasty baked potato chips in it. Those baked chips are so not worth it by the way. Just get the regular chips and eat less. I live, and I learn.
When I toss together a batch of buttermilk dressing, I don't add mayonnaise and I don't add cornstarch. I thicken mine with IMO, that imitation sour cream often used by the lactose intolerant. I use it because it's more stiff than regular sour cream, and I like that you can keep a tub in the fridge for 6 months and it never goes bad! Great for those of us who don't use it very often. Anyway, I have seen some recipes that call for thickening the buttermilk on the stove with a little cornstarch. I have never tried that method. Here is how I do it:
1 cup buttermilk
1/2 cup IMO imitation sour cream (or regular sour cream will work too)
1/2 cup crumbled blue cheese
1 teaspoon dried thyme
1/4 teaspoon sugar
1 teaspoon salt, more to taste
1 teaspoon coarse ground pepper, more to taste
I put it all in a stainless bowl and grab my wire whisk and twirl and twirl and twirl. Whisk until ingredients are combined and smooth. The blue cheese will still remain somewhat chunky, but the sour cream and buttermilk should be combined. Adjust seasonings to taste - I like a lot of pepper and this does need a fair amount of salt to balance the flavors. I use dried thyme because I make a batch large enough for the whole week, and fresh herbs will turn black after about 24 hours. If you make a small batch or will eat it all immediately, be my guest and use fresh. Dressing will thicken over the next few hours in the refrigerator.