Trim broccoli and chop by hand into smaller pieces, you can use the stem (peel it first), or not, to your preference. Toss broccoli with almonds, cranberries and most of red onion in large bowl. Meanwhile, whisk buttermilk, mayo, vinegar, sugar and a pinch each of salt and pepper in small bowl. Pour dressing over broccoli (if you've skipped the stems, you might not want it use it all) and toss well. Season well with salt and pepper to taste. Slaw should keep up to a week in the fridge.