In a large non-stick skillet, cook the bacon over medium heat until crisp. Transfer the bacon to a paper towel lined plate to drain. Discard the bacon grease and lightly wipe out the skillet with clean paper towels.
Add the butter and vegetable oil to the skillet and heat over medium-high. When the foaming subsides, add the brown sugar and salt and stir until dissolved. Add the onions and stir to combine. Cook, stirring frequently, until the onions start to soften, about 5 minutes. Reduce the heat to medium / medium-low and continue cooking, stirring occasionally, until the onions are softened and dark brown in color, about 30 minutes. Set aside to cool slightly.
Preheat oven to 425° F. Lightly grease a 1-quart baking dish. Set aside.
Reserve ¼ cup of the shredded Gruyére and set aside. In a medium mixing bowl combine the remaining cheese, mayonnaise, sour cream, pepper, crushed red pepper, and 1 tablespoon of the chives. Mix well until blended. Finely chop 3 slices of bacon and add to the cheese mixture. Reserve the remaining bacon for topping.
Add the caramelized onions to the cheese and bacon mixture. Fold together until combined. Transfer the onion mixture to the prepared baking dish. Top with the remaining chopped bacon, and the reserved cheese.
Bake for 20 to 25 minutes or until browned and bubbly. To serve, sprinkle with the remaining chives.
Serve with thick sliced, toasted bread, crisp vegetables and/or hearty crackers.