Ancho chiles are a type of dried chile pepper commonly used in Mexican and Southwestern U.S. cuisine.
The pepper is the dried version of is the poblano pepper. To be specific, it's the dried version of the ripe version of the poblano pepper.
In other words, the chiles we know as poblano peppers are fresh chiles that are harvested before ripening, which is why they're green. It's what your basic chile Relleno is made with.
But when allowed to ripen, poblanos turn red and develop additional sweetness, which in turn balances out their already mild heat. Thus anchos are red while poblanos are green.
Incidentally, the word ancho translates to "wide" in English, while poblano refers to the state of Puebla in central Mexico where the peppers are supposed to originate.
Using Ancho Chiles
So ancho chiles are what you get when you dry poblanos, and it's done for the purpose of preserving them.
Ancho chiles can be reconstituted by soaking them in warm water, or they can be ground up or crushed and added to a recipe in that fashion.
Drying the chiles doesn't affect their heat, although the way the heat is transmitted will depend on how finely crumbled/ground they are, and whether they're reconstituted first or not. In other words, crumbled up chiles will give you a more localized spiciness whenever you happen to get a piece in a particular bite.
Or you might get several. Whereas ones that are reconstituted first and then puréed will disperse their heat more evenly throughout.
Ancho chiles have a deep red color and a wrinkled skin. Sweet and smoky with a flavor slightly reminiscent of raisins, their heat is mild to medium-hot.
You could also use a spice grinder to grind dried ancho chiles into a powder to use in spice rubs or for making mole, enchilada sauce, and chili.
Make Ancho Sour Cream
Ancho sour cream will change your life, but only if you use full fat sour cream. (If you use reduced-fat sour cream, it will still taste really good, but your life will stay the same.) Soak the dried pods in hot water for 30 minutes, then remove the seeds and stems. Combine the reconstituted peppers with some sour cream and purée until smooth.
Serve it with baked potatoes or stir it into mashed potatoes or basically, anywhere you already use sour cream.
You could also use a similar approach to make a spicy ancho cream sauce to serve with enchiladas — but instead of sour cream, use Mexican crema.
Ancho chiles register between 1,000 and 2,000 Scoville heat units, which means they're quite mild.
They're sometimes incorrectly referred to pasilla pepper (as are poblanos, for that matter) but they're not the same thing. Indeed, I've come across recipes that referred to anchos as the fresh version and poblano as the dried.
Finally, because believe it or not, I do get questions about it, a note on the spelling of the word chile. When you're talking about the peppers, jalapenos and so forth, it's chile. When you're talking about the thing you make with stewed meat and beans and spices, that's chili.
And if you're talking about the nation that happens to be the longest in the world when measured north to south, which also happens to be one of the world's top wine producers, then you mean Chile.