How to Make It
In a medium saucepan, cook the barley in salted boiling water until al dente, 30 minutes. Drain well and transfer to a large bowl. Let cool slightly.
Meanwhile, in a small skillet, toast the pine nuts over low heat, stirring, until lightly golden, 3 to 5 minutes.
In a small skillet, heat 2 tablespoons of the olive oil. Add the currants and shallot and cook over moderate heat, stirring, until the shallot is golden, about 3 minutes. Scrape into the barley and add the pine nuts.
In a food processor, pulse two-thirds of the kale with the lemon juice until chopped. With the machine on, slowly drizzle in the remaining 1/2 cup of olive oil until smooth. Season with salt. Scrape the pesto into the barley. Add the preserved lemon, if using, and the remaining kale leaves, season with salt and toss well. Serve.