For a mellower flavor, make the dressing a day ahead.
In a blender or food processor, combine yogurt, mayonnaise, sesame oil, vinegar, and onion. Puree until smooth. Add celery seed, peppers, salt, and sugar, and blend for a few seconds to combine.
Remove large outer leaves from cabbages and save to line the serving bowl. Shred cabbages with a large knife and set aside. Peel and grate carrots, or julienne them on a mandoline. Set aside.
Melt butter in a small saute pan and add peanuts. Toast, shaking pan frequently, until brown. Do not burn. Let cool.
In a large bowl, combine shredded cabbages and grated carrots. Add dressing; mix well. Crush peanuts slightly with the side of a knife and, just before serving, add three quarters of them.
Line serving bowl with reserved cabbage leaves and fill with coleslaw. Garnish with remaining peanuts, and serve immediately.