Season the beef chunks with a few pinches of kosher salt and some black pepper. Melt and heat the butter in a large sauté pan then add the beef chunks. Let the brown undisturbed for a few minutes on one side, turn, then repeat. Remove from heat.
Add to your slow cooker: the cubed squash, browned meat, lemon juice, thyme, rosemary, broth, and salt. Let it cook for 6-8 hours on low. Be careful not to stir the stew so that the delicate squash cubes maintain their shape.
Discard the cooked herbs and plate ladles of the stew with a sprinkling of fresh chopped curly parsley.