Add sugar, powdered pectin and kosher salt to a medium bowl, whisking to combine.

In a medium saucepan, add sherry vinegar, rice wine vinegar, coriander and cardamom. Bring to a boil over medium heat. As soon as the mixture comes to a boil, remove from the heat and fish out the cardamom and coriander. Discard the spices.

Add the sugar to the saucepan and warm over medium heat, stirring with a wooden spoon until combined. The mixture will seem dry at first; just keep stirring and everything will eventually moisten up (similar to wet sand). Add the quartered strawberries and continue to stir, using your wooden spoon to crush and break up the berries. Continue to stir and crush until the mixture turns to liquid and comes to a boil. Continue to boil until thickened, stirring constantly (about 5 minutes).

Transfer the jam to a heat-proof bowl and let cool completely. Pour into jars, seal and store in the refrigerator.