Start by heating a medium pan to medium high heat. Add the olive oil, thinly sliced onions, and a pinch of salt to the pan. Let caramelize for about 20 minutes stirring often. The onions are finished when they are soft and a golden brown color.
Assemble the grilled cheese by spreading the brie on one slice of bread. Then layer the sliced pears, carmalized onions, a drizzle of honey, a punch of salt and arugula. Top with the second slice of bread, then spread a thin layer of butter on the outside of the bread.
To cook heat a pan to medium high. Ensure the pan is hot before placing the grilled cheese on the pan buttered side down. Let cook about 3 mintues until the bread has started to brown and devolop a crunchy exterior. Butter the other slice of bread and flip. Apply pressure to the sandwchich with a spatula or heavy pan to ensure all the ingredients are held together tightly. Remove from the heat, slice in half and enjoy!
The amount of brie and butter will vary based on the size of your bread slices so be sure to add more or less to get even coverage.