A creamy, savoury gratin that’s so much more than the sum of its parts

A few years ago, my recipe tester Hannah rang me to rave about a celeriac and lentil gratin she’d made from Jenny Chandler’s book Pulse. I made it, then Hugh, my husband, made it, and then the friends we’d cooked it for also made it. Conclusion: people love it. Staring at a gnarly celeriac, some tins of tomatoes and lentils, plus a couple of handfuls of cashews, you’d never imagine they’d create something so moreish. But that’s the strength of great knowhow (Jenny’s) and the transformative power of time and heat on even the most simple of ingredients.