Spread chilies onto a baking sheet and roast in a 375 Fahrenheit oven until chilies become aromatic and darken in color, about 6-10 minutes. Allow chilies to cool.
Remove stems and seeds after chilies have cooled.
Grind chilies using a mortar and pestle or spice grinder to desired consistency.
Store chili powder in an air-tight container for up to a week.