Methods 1) Fry the aubergine in the olive oil, in batches if necessary, until golden brown. 2) Add the tomato passata to the aubergine and bring to the boil. Set aside. 3) Meanwhile, mix together the spinach and ricotta in a bowl. Add the egg and stir well. 4) Using your fingers push the spinach mixture into the pasta shells. Place the shells in a slow cooker, layering if necessary. 5) Pour over the tomato and aubergine mix and cook on high for 4 hours. Serves 3.