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Combine mustard seed, coriander, crushed red pepper, salt, and pepper in a small bowl. Set aside.
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Remove corn kernels from ears of corn until it measures 4 cups (about 3-4 large ears). Set aside.
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Finely chop or process in a food processor the red pepper, jalapeno, and red onion and set aside.
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Mix the cornstarch and water together in a small bowl to create a slurry and set aside.
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In a medium saucepan, bring vinegar, white sugar, and water to a boil to dissolve the sugar.
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Add spice mix, red pepper, jalapeno pepper, and red onion. Bring to a boil.
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Add the corn kernels and return the mixture to a boil, then reduce heat to medium-low and simmer for 10 minutes.
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Optional: Using an immersion blender, pulse the mixture about 10 times, or just until broken down slightly, but still chunky enough that you can recognize the pieces. (Alternately, if you don't have an immersion blender, remove 1/3 of the mixture and process lightly in a food processor or even blender. Again, don't process so much that you can't recognize the various parts of the salsa).
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Add 2 Tbsp of the cornstarch//water mixture and simmer about 2 minutes more. If necessary, add another 1-2 Tbsp of the cornstarch until the liquid thickens nicely. The corn you just added no longer tastes raw (should taste "fresh", but not raw).
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Let the salsa cool before packing it in jars or a container.
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Let the salsa chill in the fridge overnight or 24 hours to let the flavors meld.
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Serve with tortilla chips or over grilled chicken.