If using regular yogurt, place it in a strainer lined with paper towel and set the strainer over a bowl. Let the yogurt drain and thicken for 20 minutes.
Preheat oven to 300 degrees F. Place sunflower seeds and 1/4 teaspoon salt on a rimmed baking sheet and shake to combine. Toast seeds until aromatic, about 10 minutes. Cool and reserve.
Combine yogurt, buttermilk, lemon juice, mayonnaise, mustard, 1/2 teaspoon salt and pepper. Whisk to incorporate and reserve.
Peel tough outer layer of broccoli stalks and trim off 1/4 inch from bottoms of stalks (should be about 3/4 of a pound. tender broccoli stalks remaining). Shred stalks in food processor, then shred carrots. Combine shredded broccoli and carrots with dressing and toss to combine. Sprinkle with sunflower seeds and serve.
2008 Ellie Krieger, All Rights Reserved