Toss the kale with 1 tablespoon oil and use your hands to massage it evenly into the kale. Spread in 1 layer on a baking sheet and season with salt. Bake until crispy, about 20 minutes. Let cool completely.
Transfer the kale to a food processor and process until it forms a fine powder.
Heat the remaining 3 tablespoons olive oil in a saucepan over medium-high heat. Add 3 popcorn kernels and cover. When the kernels pop, add the remaining kernels, cover partially and heat until they start popping. Cook, shaking the pan frequently, until the popping slows almost to a stop.
Pour the popcorn into a bowl, drizzle with the butter, add the kale powder and season with salt. Toss to evenly coat the popcorn. Enjoy!