Peel and quarter the parsnips. Peel the carrots and cut into bite-sized pieces. Core and roughly dice the butternut squash. Wash the potatoes. Peel the onion and cut into cubes. In a small bowl, mix the flour with salt and pepper.
Preheat the oven to 160 °C (320 °F).
Melt the butter with a splash of olive oil in a large saucepan over medium heat. Add the onion and sage leaves and cook for 3-4 minutes until softened. Add the tomato paste and cook for 1-2 minutes, stirring frequently.
Coat the beef in the seasoned flour. Add the coated beef to the saucepan along with the parsnips, carrots, butternut squash, potatoes, red wine, and vegetable stock. Stir well to combine. Season with black pepper and salt to taste. Bring to a boil over medium-high heat, then cover with a lid and transfer to the preheated oven. Braise for 3-4 hours until the beef is very tender and shreds easily when pressed with a fork.
While the ragout is braising, prepare the gremolata: grate the lemon zest, finely chop the rosemary and garlic clove, and mix together.
Sprinkle the gremolata over the ragout just before serving. If needed, keep the finished ragout warm in the oven at 110 °C (230 °F).