Preheat the oven to 400 degrees F.
Poke holes in the sweet potato halves with a fork. Place on a parchment- or foil-lined baking sheet and bake until fork tender, about 1 hour. Alternatively, microwave on high until the flesh is fork tender, 6 to 8 minutes. Set aside.
Tie the sage, thyme and rosemary sprigs together with kitchen twine or a clean rubber band and set aside.
Heat a Dutch oven over medium heat and cook the bacon, stirring often, until crisp, about 10 minutes. Use a slotted spoon to transfer the bacon to a paper-towel-lined plate and discard all but 1 tablespoon of the pan drippings.
Pat the beef dry and sprinkle with salt and pepper. Return the Dutch oven to the stovetop on medium-high heat. Working in batches, brown the meat on all sides, 5 to 7 minutes. Add the broth, onions, carrots, celery, tomato paste, garlic and herb bundle. Bring to a boil, then reduce to a simmer. Cover and cook for 1 hour on low heat.
Uncover and cook at a low simmer until the meat is tender and the vegetables are cooked through, 45 minutes.
Scoop out the flesh from the cooked sweet potatoes and place in a blender. Carefully add 1 cup of the stewing liquid and the cashew butter to the blender, then puree until smooth. Add the puree to the stew and stir well. Simmer to thicken, 5 minutes, then season with salt and pepper. Remove the herb bundle and serve the stew garnished with the bacon bits and parsley leaves.