Method:
- Preheat the oven to 200°C/fan180°C/gas 6. - In a saucepan, bring 200ml vegetable stock to the boil with 2 garlic cloves, lightly crushed, then remove from the heat and stir in 200ml double cream. Set aside to cool and infuse. - Meanwhile, heat 1 tbsp olive oil in a pan and gently fry 1 large, finely chopped onion, for 10 minutes, until very soft. - Peel and quarter 1 large celeriac, then slice to 3mm thickness. Put in a bowl with 3 medium potatoes, sliced to 3mm thickness. Toss with 1 tbsp plain flour, 1 tbsp chopped fresh flatleaf parsley and season. - Butter a 1.2-litre ovenproof dish and layer up the celeriac, potatoes and the softened onion. Strain the cream mixture (discard the garlic) into a jug and pour over the gratin. - Bake for 1-1¼ hours, until golden brown and bubbling and the potatoes are cooked through.
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