Cook bacon in a large 4-qt. saucepan or Dutch oven. Drain bacon on paper towels and set aside. Drain all but 1 Tbsp. bacon drippings.
Cook onion, apple, sage, garlic and cayenne, if desired, in reserved over medium-high heat about 5 to 7 minutes or until onion is softened and translucent, stirring frequently.
Transfer onion mixture to a blender; add 2 cups broth and purée until smooth. (Or, use an immersion blender to purée right in the saucepan.) Return purée to saucepan and add remaining broth, pumpkin and brown sugar. Bring to a boil over high heat. Reduce heat to medium and simmer 10 minutes, stirring occasionally. Season to taste with salt and pepper. Serve topped with bacon and other optional toppings, as desired.