Heat the chicken broth in a medium saucepot over high heat, seasoning it generously with salt. Add the chicken thighs to the pan and bring the broth to a simmer. Cover, and reduce the heat to low. Simmer gently until the chicken is tender, about 40 minutes. Remove the thighs from the liquid, pat them dry, and set them aside on a platter; cover it with foil to keep them warm.
While the chicken is cooking, pour the grapeseed oil into a large pot with high sides, and bring it to 400˚F over high heat. Set a wire rack in a rimmed baking sheet or over several layers of paper towels (for draining chicken). In a shallow dish, combine the flour with the paprika, celery salt, black pepper, 1 teaspoon salt, and the cayenne. Use a whisk to thoroughly combine the ingredients.