First, you’re going to sear the lamb roast to develop a nice golden crust. That’s where the flavor really shines. To do that, dry the lamb very well with paper towel and season with a couple generous pinches of salt and pepper. Heat a cast iron skillet over high heat, then add the ghee. You want the pan smoking hot. If not, the meat will steam instead of sear. Try for 3 to 4 minutes a side until you get most of the roast seared. Remove the meat from the pan (I put it on a plate), then reduce the heat to medium, and add the chicken broth, scraping up the brown bits from the bottom of the pan.
Place the roast in the slow cooker.
In a small bowl, mix the garlic, rosemary, thyme and mustard. Pour it on top of the lamb and use your hands to coat the meat with the mixture.
Toss the chopped root veggies (carrots, parsnips, potato and rutabaga) with salt and pepper, and arrange them around the meat. Pour the chicken broth from when you deglazed the pan on top of the veggies.
Cook on low for 8 to 10 hours.
Serve with a green salad or veggie of your choice for a complete meal.