Trim and peel the onion, then cut into thin (approximately 1/8”) slices.
Melt the 1 1/2 tablespoons of butter in a wide, flat pan over medium-low heat. Add the onion slices and a generous pinch of salt.
Cook the onions over medium-low heat, stirring regularly, until they achieve your desired color. This can range anywhere from 40 to 60+ minutes depending on the temperature and how dark and caramelized you want them.