Melt the butter and oil in a large deep pot over medium heat. Add the onions and saute until slightly softened, 2 to 3 minutes, then add the garlic and cook for 2 minutes more. Add 1 1/2 cups vegetable stock to the pot along with the ginger and bring to a simmer. Add the collard greens in batches, stirring and adding more as they wilt down. Stir in the honey and season the pot with salt and pepper. Stir in the tomatoes, then cover and cook, adding more stock if necessary, until the greens are tender, about 20 minutes. Taste the greens and add salt and pepper if you like.