Heat the oven to 200°C. Bring the stock, which should not be too salty, to the boil in a medium-sized pan and throw in the chard stalks, bay leaves and garlic. Cook for 15 minutes and drain over a bowl to catch the stock.
Make a béchamel sauce; melt the butter in a small pan, then add the flour, over a low heat. Let it cook for a minute or two without browning, and add the milk gradually, stirring until it is smooth after each addition. Add
Retrieve the cloves of garlic and chop them finely, then add chard stalks and garlic to the béchamel sauce, cook for 3–4 minutes and transfer to a cazuela or an oval gratin dish. Sprinkle with cheese and bake for 25–30 minutes until the top is browned and bubbling.