Mediterranean bean stew with potato griddle cakes

Name: Mediterranean bean stew with potato griddle cakes
Ingredients: 2 tbsp extra-virgin olive oil, plus extra to serve; 2 red onions cut into wedges; 2 courgettes, chopped into 1cm/½in batons; 150g/5½oz celeriac, cut into cubes; 1 garlic clove, finely chopped; 2 tbsp tomato purée; 1 tbsp smoked paprika; 1 x 440g/1lb tin chopped tomatoes; 200ml/7fl oz vegetable stock; 1 x 400g/14oz tin butter beans or mixed beans, drained; handful fresh basil; 1 lemon, zest only; 100g/3½oz cooked broad beans; 250g/9oz mashed potatoes; 1 tsp baking powder; 100g/3½oz plain flour; salt and freshly ground black pepper; 1 tbsp fresh thyme; 2 tbsp vegetable oil