Trim any excess fat from the Lamb Shoulder and cut into 1–1.5 inch cubes; pat the pieces dry with paper towels and set aside.
Peel and thinly slice the Onion; mince the Garlic and grate or finely chop the Ginger.
Heat 2–3 tablespoons of Niter Kibbeh in a heavy pot over medium heat until it shimmers.
Add the sliced Onion and sauté until translucent and just starting to golden, about 6–8 minutes; then stir in the minced Garlic and Ginger and cook for another 1–2 minutes until fragrant.
Increase the heat to medium-high, add the prepared Lamb Shoulder to the pot and brown the pieces on all sides, about 6–8 minutes, working in batches if needed so they sear rather than steam.
Return all the browned lamb to the pot and sprinkle in the Ground Turmeric, Salt, and Ground Black Pepper; stir well so the spices coat the meat and cook for 1 minute to bloom the turmeric.
Pour in about 2–3 cups of Water (enough to barely cover the meat), bring to a gentle simmer, then reduce the heat to low, cover, and cook until the lamb is beginning to tenderize, about 45–60 minutes depending on size of pieces.
Peel and cut the Potato into large chunks and slice the Carrot into thick rounds; add them to the pot, stir gently, and continue simmering uncovered until the vegetables and lamb are tender, about 20–30 minutes more. Taste and adjust seasoning if needed.
If the sauce is too thin, raise the heat and reduce a few minutes to concentrate flavor; if too thick, add a splash more Water and warm through.
Serve the Yebeg Alicha hot family-style on Injera, spooning generous portions of lamb, vegetables, and sauce onto the flatbread for scooping.
