Whole-roasted celeriac with coriander seed oil

I’ve managed to achieve the seemingly impossible here, of taking a recipe from my NOPI cookbook (full of recipes which would not make it into Ottolenghi SIMPLE) and actually making it more complicated for Ottolenghi SIMPLE. In NOPI, the celeriac is roasted whole as it is, for 3 hours, brushed with oil and sprinkled with salt. The results are so delicious and so straightforward that I’ve taken the liberty of adding one more twist in the form of the coriander seeds