Celeriac in Lemon Sauce

• 1–1½ lb (450–700 g) celeriac

Remove the thick outer peel of the celeriac and cut celeriac in thick slices, then cut each slice into strips like large chips. Add to a pan of boiling salted water and simmer gently for about 10 minutes until just tender. (Test with a knife tip; if overcooked, celeriac will be soggy.)

Meanwhile, make the sauce. Melt the butter in a saucepan over low heat and stir in the flour. Cook gen