Brush the salmon lightly with olive oil, and season with salt and
pepper. Line a grill pan with foil and
lay the salmon on top.
Place the celeriac in a pan with cold water to cover. Salt and
bring to the boil. Lower the heat,
cover and simmer for 12-15
minutes until tender.
Preheat the grill to medium.
Whisk together the mustard, lemon
juice, a pinch of sugar, salt, pepper
and 1 tbsp olive oil.
Grill the salmon for five minutes
on each side. Meanwhile, drain the
celeriac, reserving 1 tbsp cooking
water. Return the celeriac to the
pan. Mash until fairly smooth. Add
the spinach, stirring occasionally
over a low heat, until wilted. Stir in
1 tbsp mustard dressing and the
reserved cooking water. Season.
Spoon the mash on to two warm
plates and top each with a fillet.
Drizzle over the leftover dressing.