450g/1lb peeled celeriac, chopped into 1–2cm/½–¾in thick, small wedges
2 leeks, trimmed and cut into 2cm/¾in chunks
1 onion, chopped
100g/3½oz baby spinach
1 tbsp chopped fresh tarragon
2 tbsp chopped fresh tarragon, plus a little extra to serve if preferred
1 tsp English mustard powder
400g tin cannellini beans, drained and rinsed
25g/1oz plain flour
2 tbsp wholegrain mustard
½ tsp baking powder
4 bay leaves
1 tbsp olive oil
¼ tsp salt
150²µ/5½´Ç³ú self-raising flour, plus extra for rolling
900ml/1½ pint vegetable stock
2 tbsp butter
25g/1oz cold butter, diced
75g/2¾ oz natural yoghurt
150ml/5fl oz apple juice