Curried celeriac slaw

In a large bowl use a fork to mix together the mustard and ½ the lemon juice. Put the remaining juice in a small bowl and add the onion and a pinch of salt, mixing and scrunching it together in your hands so that it begins to soften; set aside. Cut the celeriac into matchsticks (this can be done with a mandolin if you have one) or grate it in a food processor. Tip into the mustard mixture and stir together well. Cut the apples into matchsticks and add to the bowl with the salt, yogurt, mayonnaise, honey, curry powder, cumin, flaked almonds and oil, plus most of the coriander. Drain the red onion and add it to the bowl, mixing everything until well combined. Season again if necessary. Scatter the remaining coriander over the top before serving.