Meanwhile, in a large pot, melt the butter in the remaining 1/4 cup of olive oil. Add the onions, season with salt and cook over moderately high heat, stirring occasionally, until softened and just starting to brown, 8 to 10 minutes. Add the chopped kale and cook, stirring occasionally, until wilted, about 5 minutes. Add the cream and honey and bring to a simmer. Cover and cook over moderate heat, stirring occasionally, until the kale is very tender and coated in a thick sauce, 35 to 40 minutes.