Step 1

Melt the butter in a large pan with the vegetable oil, then add the celeriac and a large pinch of salt. Cut a round piece of baking paper the same size as the pan and use to cover the celeriac. Cook gently for 20 minutes, stirring regularly, until the celeriac is very soft and starting to collapse. If it starts to stick, add a splash of water to the pan.

Step 2

Meanwhile, bring the double cream to the boil in a small pan.

Step 3

Tip the celeriac and butter into a food processor and whizz until smooth. Add the double cream, a splash at a time, between blends, until it is a light puréed consistency. Season and push through a fine sieve. Reheat to serve.