If you haven't had butter beans before, do yourself a favor: Find some, buy some, eat some. Delicious. Like Buttah. If you must substitute, I guess cannelini would be okay. But not quite "Like Buttah".
1 bunch Swiss Chard, leaves stripped from stems
8 oz cremini mushrooms, quartered
2 tablespoons tomato paste
1 can butter beans, drained and rinsed
Loads of freshly ground black pepper
Heat a medium saute pan over high heat. Chop the chard stems into bite-sized pieces, about the same size as the butter beans. The mushrooms should also be about this size. Add the chard and mushrooms to the hot pan and cook until they start to darken, just a few minutes. Add the tomato paste and a couple tablespoons of water to the pan, lower heat to medium, and continue cooking until stems soften, about 5 minutes. In the mean time, slice the chard leaves. Once the stems are soft, add the leaves to the pan and cover. Cook just until the leaves wilt, about a minute or two. If needed, add another couple of tablespoons of water to prevent burning.
Toss beans with the black pepper. Serve a big heap of the chard mix with a few big spoonfuls of beans. Enjoy.
Combine leftover beans and chard for next day's lunch. Or serve with whole wheat pasta for a hearty dinner.