INSTRUCTIONSPlace the oil, a pinch of salt, and the sliced onion in a pan over low heat, stirring to coat. Continue to cook, stirring occasionally, until the onion slices are soft, golden brown, and caramelized, about 25-30 minutes.
Spread one side of each of the bread slices with the softened butter. On the other side, layer 1/2 the cheese slices, the ham slices, and the caramelized onions followed by the rest of the cheese.