Brown and crisp bacon in a Dutch oven pot over medium-high heat for 3-4 minutes. Turn off heat, transfer bacon to a large bowl, and reserve bacon fat in the pot.

Season lamb meat cubes with salt and black pepper to taste. Add lamb into the Dutch oven pot with the bacon fat over high heat, sear all sides of the lamb cubes until browned (about 5 minutes). Ensure not to overcrowd the pot with lamb, as it may steam instead of sear. You may need to repeat this process a couple of times. Transfer lamb to the same bowl you placed the cooked bacon, leaving fat in the pot.

Reduce heat to medium; add onions and stir until lightly browned, seasoning with a pinch of salt. Add garlic and cook for about 1 minute.

Pour beer into the pot. Stir for about 3 minutes until the beer has dissolved any browned bits from the bottom of the pot.

Add the meat and bacon back to the pot. Add tomato paste, carrots, celery, thyme sprigs, sugar, more salt and black pepper to taste, and enough chicken broth to cover the meat and the veggies.

Bring the stew to a gentle simmer, then reduce heat to low, cover the pot, and simmer until the lamb is fork-tender, about 2 hours. Stir occasionally and, if desired, skim off any excess fat.