*NOTE: When asking your butcher to cube your lamb, ask him/her to saw one or two leg bone pieces for you (about a 2-inch length). Put this in the stew while it is cooking. Not only does the marrow add flavor to the stew, but when you go to remove the bones before serving, the chef (you!) gets a little nom of some well-seasoned cooked marrow as a side treat.
In a gallon plastic bag, place arrowroot. Add lamb cubes and shake until all of the meat is coated.
In a Dutch Oven (or heavy-bottomed pot), melt bacon grease on medium-high heat. Add lamb cubes and brown on all sides. Remove meat from the pot and set aside.
Add butter and onions to the Dutch Oven. Scrape the brown bits off of the bottom while cooking the onions over medium (adds so much flavor). Add broth and water, continuing to scrape the cooked bits off of the bottom. Add lamb. Bring to a boil. Reduce to a simmer and let cook for 45 minutes.
Add carrots, parsnips, asparagus, thyme, salt and pepper. Either cook for one hour on simmer for an hour and a half until ready to serve or you can transfer to a crock pot (this is what I did). I had some errands to run, so I transferred the mixture to my crock pot and cooked this on low for 3 hours to let all of the flavors marry together and allow the veggies to really become tender. Before serving, taste for possible addition of salt and pepper. Season as needed.
Transfer to soup bowls and add optional thyme leaves for garnish.