The slow cooker will do most of the caramelizing for you, but thinner slices soften and sweeten more evenly.
Brown the sausages (optional but recommended): In a large skillet over medium-high heat, sear the sausages for 2–3 minutes per side until nicely browned but not cooked through. This step builds deeper flavor and gives the finished dish that rich, dark look. If you’re short on time, you can skip this and add the sausages straight to the slow cooker.
Layer the onions
