Cerámica de barro is a type of glazed terra cotta earthenware traditionally used both for cooking and tableware in Spain. The cazuela de barro--the round vessels in the picture above--can be used in the oven, on the stove top (gas, electric coil, or smoothtop), or even in the microwave. They also make a nice presentation at the table.
Nothing says "This is Spanish Food" like a cazuela de barro. Even the paella pan, though far better known outside of Spain, is really a regional thing, originally from Valencia, and used only for rice, but casseroles, pots, plates, and bowls made of glazed clay, or barro, are used all over the country in countless ways.
In Galicia, where Ana's family is from, even the traditional punch bowls, used for making flaming queimada, are made from glazed terra cotta.
We usually buy all of our clay kitchen and tableware at arts and crafts festivals when we're in Spain. The Feria Mercado de Artesanía, which takes place around Christmastime in Madrid, is one of our favorites.
Here in the U.S. the Spanish on-line food store La Tienda has a good selection of cazuelas and other Spanish-style earthenware to choose from.
A good cazuela is tough and lasts a long time. But if you're cooking with a cazuela, there are a few things you need to remember to make it last. First, always soak the cazuela in water for twenty four hours before using it. When using a cazuela on the stovetop, heat it gradually, on low or medium heat, not high. Finally, when you're done cooking, let the cazuela cool before putting it in the sink or getting cold water on it. All of this helps to prevent the cauzela from cracking. Otherwise cazuelas are easy to care for and really quite inexpensive.
They also come in colors. These in the picture below are for the table, not cooking, though I have seen bright red cooking cazuelas too recently.
Some of the best dishes to make in a cazuela are eggs in tomato sauce (huevos con tomate) and salt cod in tomato sauce (bacalao en sals de tomate). There are many, many others. Use the smaller ones for toasting nuts, or serving all sorts of tapas.