Ancho chiles
A dried ripe poblano pepper, broad, wrinkled and nearly black-red, with mild heat and a sweet flavour of raisins and cocoa.
Ancho is the dried form of the ripe, red poblano and one of the most widely used dried chiles in Mexico. The pods are leathery and pliable, the heat is low, and the flavour is fruity and sweet with hints of prunes, raisins and coffee. What matters in cooking is that it gives a sauce not only flavour but also colour and body, which is why it is usually toasted briefly, seeded, soaked and puréed for mole, adobo or enchilada sauces. Good pods are still soft and fragrant; brittle, dusty ones are old. They are sold in Latin American grocers, by mail-order spice and chile suppliers and in well-stocked supermarkets, more commonly in the English-speaking world than in German-speaking countries.
Substitute:
The closest match is mulato, a darker, more chocolatey dried form of the same poblano; pasilla or guajillo also work, pasilla being more bitter, guajillo brighter, tangier and a little hotter. Ground ancho powder gives the flavour but not the smooth body of a puréed pod. Sweet paprika with a little mild chili powder is only a stopgap: the colour and warmth are roughly right, but the raisin sweetness and body are missing.