Caramelize the onions: thinly slice 1-2 yellow onions, then cook in 1 tbsp butter and 1 tbsp olive oil with a pinch of salt until caramelized.
Whip the goat cheese: combine 4 oz goat cheese with 1-2 tbsp heavy cream, a squeeze of fresh lemon juice, salt, and pepper until smooth.
Assemble the sandwich: spread whipped goat cheese on sourdough bread. Layer with Fontina cheese, caramelized onions, fig jam, and crispy bacon. Add arugula and top with balsamic glaze.
Grill the sandwich until golden brown and cheese is melted.
