Remove one to two outer layers of lettuce leaves, discard.Place the lettuce on a cutting board, cut off the stem end, discard.Cut each head of lettuce in half, then quarter.Gently rinse the lettuce under cold water.Gently shake the lettuce leaves so the water drains into the sink.Place the washed leaves onto a paper towel lined pan, cut side down. Let lettuce drain, change paper towel if necessary. Place in refrigerator.Mix buttermilk,mayo, vinegar, garlic, salt, pepper and white parts of green onion in a blender on high speed until smooth. Refrigerate until ready to serve.When ready to serve, place the lettuce wedges on a plate or platter. Drizzle with dressing, top with grated cheese, bacon, green onions, etc.