Salmon with celeriac gratin & green beans

A lean fish supper with an alternative dauphinoise made with mild celeriac. Wholegrain mustard makes a tangy glaze for the salmon.

Heat oven to 200C/180C fan/gas 6. Slice the celeriac as thinly as you can – quartering it first will help. Find a baking dish that will hold all the celeriac, then add a layer before scattering with some garlic, thyme and seasoning. Repeat layers, finishing on a celeriac layer.
Mix the stock cube with 450ml boiling water, season with nutmeg, then pour over the celeriac. Bake for about 1 hr 15 mins – pressing the celeriac into the dish so that it stays submerged and soaks up the stock – until a skewer poked in goes in easily, and the top is crisp.
When the gratin has 15 mins to go, sit the salmon on a baking parchment-lined baking sheet. Mix the mustard with some ground black pepper and a little salt, and brush over the fillets. Bake with the gratin for 12-15 mins until cooked just through.
Meanwhile, cook the beans in boiling water until tender, drain well and season. Divide into 4 equal portions along with the gratin, and serve with the salmon.