Cook the bacon in a small nonstick skillet over medium-low heat until crispy, about 8 minutes. Transfer to a paper-towel-lined plate to drain, and reserve 1 teaspoon drippings for the dressing. Finely chop the bacon strips and reserve.
Combine 1 cup water, the ice cubes and onions in a small bowl. Let the onions soak for 10 minutes while preparing the rest of the salad, and then drain and pat dry.
Whisk the buttermilk, sour cream, lemon zest and juice, reserved bacon drippings, 3/4 teaspoon kosher salt and pepper to taste in a large bowl. Add the broccoli, onions and golden raisins to the dressing. Toss well, cover and chill for at least 1 hour or up to 4 hours.
Before serving, toss well and season with additional salt and pepper. Transfer to a serving dish and top with the chopped bacon and sunflower seeds.