Place finely shredded cabbage, carrot, celery, spring onion, red onion and apple into a large bowl and toss together.
In a separate bowl, whisk together the mayonnaise, buttermilk (see tip below), lemon juice, apple cider vinegar, caster sugar and salt and pepper.
Pour the dressing over the coleslaw and mix to combine well.
Place into the fridge for at least an hour before serving.
Thermomix Method
Place the mayonnaise, buttermilk, lemon juice, apple cider vinegar, caster sugar, salt and pepper into the TM bowl. Mix on Speed 6 for 20 seconds or until well combined. Set aside.
Add the cabbage, apples, carrot, celery, spring onions and red onion to the bowl. Chop on Speed 4 for 2-3 seconds. Scrape down the sides of the bowl and repeat until the coleslaw is the consistency you would like.
Pour over the dressing and stir to combine. Refrigerate for at least one hour before serving.
Notes
Buttermilk tip: If you don't have any buttermilk - simply mix 1tsp of lemon juice or vinegar into ¼ cup of milk and you’ll have perfect buttermilk in no time.