1 chicken (1.6 kg)
1 litre (4 cups) chicken stock
30 gm butter, coarsely chopped
1 tbsp olive oil
1 large onion, finely chopped
3 garlic cloves, finely chopped
40 gm (8cm piece) finely chopped ginger
2 tsp ras el hanout (see note)
400 gm whole canned tomatoes
180 gm black lentils, rinsed
260 gm peeled celeriac (about ½), diced
Pinch of saffron threads
¼ cup each finely chopped flat-leaf parsley and coriander

To serve: thick plain yoghurt

Place chicken in a saucepan large enough to fit snugly, add stock and 500ml water or enough to just cover, season to taste, bring to the boil over medium-high heat, then reduce heat to low-medium, cover and simmer for 10 minutes.
Cool to room temperature (2-3 hours), remove chicken and coarsely shred meat (discard bones and skin). Strain stock (discard solids).
Reserve 1 litre stock (freeze remainder for another use) and meat separately.

Heat butter and oil in a saucepan over medium-high heat, add onion, cook until tender (5-10 minutes), add garlic, ginger and ras el hanout, stir until fragrant (1-2 minutes), add tomato, lentils, celeriac, saffron and reserved stock, season to taste and bring to the boil.
Reduce heat to medium, simmer until lentils are tender (20-30 minutes), add herbs, season to taste, stir in chicken and serve with a dollop of yoghurt.