Meanwhile, in 12-inch skillet, melt butter over medium heat. Add onions and 1/4 teaspoon salt; cook 4 to 5 minutes, stirring frequently, until onions brown on edges and soften. Add bell pepper; cook and stir 2 to 3 minutes or until pepper softens and begins to brown on edges. Add mushrooms; cook and stir 4 to 5 minutes or until mushrooms release juices, juices absorb and mushrooms brown. Stir in kale; cook and stir 1 to 2 minutes or until wilted. Add wine; stir constantly, scraping up browned bits, 1 to 2 minutes or until liquid is almost completely absorbed.