Step 1 Roast the chiles over the flame of your stovetop until they are black. Put them in a plastic bag and cover the bag with a warm, wet towel to steam the chiles. Let stand 10 to 15 minutes. Peel off the skins. Remove the veins and seeds very carefully, making just one cut from the stem end midway (or less) down the chile. Rinse the chiles under running water, as briefly as possible, to remove the skins.
Step 2 Cut the cheese into small logs that can be easily tucked into the chiles. Stuff the prepared chiles with the cheese as full as you can while still able to close them.
Step 3Place the oil in a big soup pot that you can serve the dish in. Add the rice and fry it for about 6 minutes, until it does not stick to the pan but slides around very easily. The rice will get only the very slightest bit of color.
Step 4Add the milk and bouillon cube to the rice and bring it to a boil, stirring to dissolve the bouillon cube. Cook for about 7 to 8 minutes, then, as the rice begins to thicken, use a slotted spoon to add the prepared chiles. (This is tricky. If you don't cook the rice enough, the chiles will swim around in the pot and may sink to the bottom, and you'll likely lose the cheese. But if you cook the rice for too long, it will become so thick that when you plop the chiles in, they'll just rest on top. You want the chiles floating in the rice, so that the rice almost completely covers them with a little green showing but they are not sitting on the bottom of the pot.)
Step 5Continue to cook the chiles and rice, uncovered, until the rice is tender. Taste the rice occasionally. If you find it is not tender but you're running out of liquid, add a little more milk and cover the pot.
Step 6Serve immediately (it's impossible to reheat). Scoop into the rice, lifting out the chiles so that each person gets a whole chile and some of the surrounding rice.