If I had to recommend a popular café, I would recommend ¨The Puddin Cafe Shop¨in Barcelona. The café is located in Avinguda Diagonal, which is a very long street near the city centre.
The local is big and there are three floors, the entrance is in middle floor. The entrance is on the middle floor, the high and low floors are only used for having a meal). On the middle floor you can also have a meal but you have to pay only there.
The decoration is about Harry Potter. On the wall there is a big picture of Hogwarts School, there are the flags of Hogwarts teams and on the door there is a big ticket of Hogwarts Express. On the low floor there are a lot of board games.
You can go there for lunch or have a snack. If you go for lunch, you can eat pasta, salads, hamburgers or sandwiches. In my opinion it is better to go for a snack because they cook delicious cakes and prepare different milkshakes and smoothies and the price is affordable.
The staff are young people who are very cheerful and efficient. They help you with your doubts about the cakes.
I hope you can go someday!