If you are walking around Clérigos, i definitely recommend you to visit Café Vitória, one of my favourite places at the moment. Located in a refurbished traditional building, on the ground floor the Café Vitória works with bar service and when the weather is ok, the garden seating is very cosy and charming. On the 1st floor, the restaurant is the best choice for a calm, pleasant and romantic dinner. I've had dinner there twice and found the food very good on both occasions. After dinner you can stay for a drink at the bar.
Rua José Falcão 156, Porto