The poblano is one of my favourite chillies but it's something I eat only rarely because I've never seen it in local supermarkets or at a wet market. Instead, I have to buy them on my annual trips to the United States, where, at least in California, the chilli is sold at all types of market, not just those catering to Mexican customers.
The chilli is quite large - about 10cm in length, not including the stem, and it has a distinctive triangular shape with an indentation at the stem end. It's usually sold when the skin is a deep, dark green, although if left to ripen (on or off the plant) it will turn red. The chilli is mildly spicy. If you find them, look for specimens with glossy, waxy, smooth skin and firm flesh. The poblano is also sold after being dried - the dark red-black, wrinkled chilli is then called the ancho.
My favourite poblano dish is chiles rellenos. It's a time-consuming dish that starts off with roasting the chillies over an open flame to char the skin, which is then peeled off. A slit is cut into the chilli so the veins and seeds can be extracted. The chilli is then stuffed - the simplest filling is cheese, which oozes out when the poblano is cooked. I make the dish using a sweet-savoury picadillo that has meat (usually beef, although I use chicken) cooked with onion, garlic, cinnamon, olives and raisins. Stuff the picadillo (or other filling) into the chilli, dredge it in flour, dip it in an egg batter then fry it so it puffs up. It's then served with a tomato sauce.
The roasted poblano can also be cut into strips, cooked with onion, garlic, cream and cheese, then wrapped in warm, soft corn tortillas, or served with potatoes or eggs.