Place the sliced onion in a small bowl with boiling water, set aside for a few minutes then drain
Rinse using cold water & pat dry using paper towels
In a large bowl, mix the mayo, mustard, sugar, vinegar, onion powder, and celery salt until all ingredients are incorporated
Mix the onion in a bowl with the cabbage and carrot, set aside
Just before serving, add the cabbage mixture and the dressing and toss to combine
