6-8 dried red chiles, such as Thai, cayenne or chile de arbol, stemmed
¼ cup firmly packed dark brown sugar
1 cup water
¼ teaspoon salt
¼ cup finely chopped fresh cilantro
Heat oil in a small saucepan over medium-high heat. Add mustard seeds, cover, and cook until the seeds have stopped popping, 20 to 30 seconds. Add mango (or pineapple), raisins and chiles to taste. (It may spatter.) Reduce the heat to medium and cook, uncovered, stirring occasionally, until the raisins are plump and the fruit is lightly browned, 5 to 8 minutes.
Add sugar and cook, stirring, until it dissolves, about 2 minutes. Add water and salt. Cook, uncovered, stirring occasionally, until the sauce is syrupy-thick, 10 to 15 minutes. Stir in cilantro and serve warm.
Make Ahead Tip: Cover and refrigerate the chutney, without the cilantro, for up to 1 week. Stir in cilantro just before serving and reheat, if desired.
Ingredient Note: Black mustard seeds are slightly stronger than the more commonly available yellow kind, the source of American ground mustard.