Preheat oven to 375 degrees Fahrenheit.
In an oven-proof skillet, heat oil on cooktop over medium-high. Prick sausages all over with a fork and add to the skillet. Cook, turning occasionally, until well browned on all sides, about 5 minutes. Transfer to a plate and set aside.
Add the sliced onion and potatoes to the skillet and season generously with salt, pepper, and nutmeg. Cook, stirring often, until onions are softened and potatoes begin to slightly brown, about 5-7 minutes.
Add the beer and bay leaf. Gently stir to combine and let simmer over medium heat for 5 minutes.
Stir the potatoes and onions again, return the sausage links to the skillet, and nestle them into the potatoes and onions.
Turn off the heat on the cooktop and place the oven-proof skillet in the oven.
Bake uncovered for 30 minutes.
Removed skillet from oven and add the drained sauerkraut to the skillet by nestling the sauerkraut between the vegetables and sausage.
Return to the oven and bake for another 5-10 minutes.
Garnish with sliced green onions and serve with your favorite mustard.