1. If you’re going to use raisins, boil for one to two minutes to plump, then drain and set aside.
2. Drain and chop the mango slices into inch-long pieces. (If using frozen mango chunks, thaw, drain, blot dry and cut into small pieces.) Set aside.
3. Combine vinegar, sugar, and salt in a large, heavy saucepan. Heat to boiling, stirring to dissolve sugar, then reduce heat and simmer 15 minutes.
4. Add garlic and ginger and simmer another 15 minutes, stirring frequently.
5. Dip about a quarter cup of liquid into a heatproof mixing cup. Add two tablespoons of cornstarch and mix to make a lump-free slurry. The amount of cornstarch needed depends on how thick or loose you like your chutney, but also varies with the mangoes. Frozen mangoes general require three tablespoons rather than two. Set the slurry aside.
6. Add the cumin, turmeric, and garam masala (or nutmeg, cloves, allspice and cinnamon).
7. Add the slurry to the saucepan and stir. After the chutney begins to thicken, cook another
minute or two, stirring continuously.
7. Remove from heat. Stir in the mangoes (and raisins, if using them).
8. Let cool to room temperature, then pour into lidded jars and store in fridge.
This chutney will last up to a month in the fridge provided the lid is on tight and you haven’t contaminated it by getting other foods on the chutney spoon.