1/2 lb Keeley's Cheese Co. Across the Pond cheese, sliced 1/2 inch thin
1 medium yellow onion, sliced
1 Tbsp canola oil
1 large handful arugula, washed (substitute baby spinach if you'd like)
1/2 tsp extra-virgin olive oil
4 Tbsp butter, room temperature, divided
4 slices hearty bread
pinch of salt
Begin cooking onions in canola oil in a medium size saute pan over high heat for 5 minutes, stirring frequently. Lower heat and cook for 20 minutes, or until onions are caramelized and sweet tasting, stirring occasionally. Add up to 2 Tbsp. of water to onions when necessary to prevent burning and sticking. Let cool.
Toss arugula or spinach with olive oil in a separate bowl.
Spread 1/2 Tbsp butter on one side of each bread slice, using 2 Tbsp. total. Begin building one sandwich by spreading 1/2 Tbsp. butter on the unbuttered side of one of the bread slices. Layer half the arugula on top of the butter, followed by half of the cheese and half of the caramelized onions. Top with another piece of bread, buttered side up. Repeat steps for second sandwich.
In a medium saute pan over low-medium heat, melt the remaining tablespoon of butter and add the sandwiches, arugula side down. Flip when the first side is golden brown, 4-5 minutes. Flip, turn heat to low, salt the top slice of bread, and wait until the second side is golden brown, about 5 minutes. Serve immediately.