Spoon oil over bottom of 4 to 6.5-quart Crock-Pot® slow cooker; add 2 tablespoons butter, distributing evenly. Add onions and apples; cover and cook on Low for 8 to 10 hours or until onions are softened and caramelized. Add broth, cider and brandy if using; season with salt and black pepper. Cover and cook on High for about 1 hour or until hot. While soup is heating, make the Gouda Cinnamon Toast. Preheat broiler. Spread remaining 2 tablespoons softened butter on one side of bread slices. Combine sugar and cinnamon and sprinkle evenly over buttered bread. Place bread on baking sheet and toas Remove from oven; turn bread over and sprinkle untoasted side with Gouda cheese. Return to broiler until cheese melts, taking care not to burn. To serve, ladle soup into bowls and float a Gouda Cinnamon Toast on top of each serving, cheese side up. Serve immediately.