Open leek & sweet potato pie

Name: Open leek & sweet potato pie
Prep time: 20 min
Cook time: 40 min
Total time: 1 h
Cuisine: European, British
Ingredients: 3 tbsp olive oil plus extra for brushing; 2 large leeks washed and sliced; 2 sweet potatoes peeled and roughly chopped into 2cm cubes; 1 tsp coriander seeds; 1 tsp chilli flakes; 2 fat garlic cloves crushed; 150g ricotta; 2 large eggs; 1 lemon zested; 100g robust leafy greens such as cavalo nero or kale, finely shredded, tough core removed; 1 small pack dill chopped; 1 pack filo pastry (around 12 sheets); 80g goat’s cheese; 1 tsp nigella seeds (optional); peppery salad to serve