Using a pot that holds at least 5 quarts, bring 12 cups of water to a boil. Once it is rolling vigorously, salt the water generously and add the farro.
Cook the farro for 10-12 minutes, until it is nearly tender. Add the chopped kale to the pot and put it down into the water with a wooden spoon. Cook for another 2-3 minutes, until the farro is tender and the kale is bright green. Drain well, rinse briefly with cool water, and then drain again.
Return the cooked farro and kale to the pot and add the raisins, olive oil, and red wine vinegar. Stir to combine.
Once the salad is at room temperature, stir in the feta. Taste, add salt and pepper as needed, and taste again.
Serve either at room temperature or chilled.