Cut bacon strips into thirds. Wrap each third around a water chestnut and secure with a toothpick. Place in an ungreased 15x10x1 baking pan or square pan. Bake until bacon is crisp, about 25 minutes.
While bacon-wrapped chestnuts crisp in the oven, in a small saucepan, combine ketchup and brown sugar. Stir the mixture over medium heat until the sugar has dissolved.
Once the 25 minutes are up, place the bacon-wrapped chestnuts on a paper towel-lined plate to drain. Then dip in the ketchup mixture. Place in a lightly greased 9x13 baking dish. Spoon any remaining ketchup sauce over the chestnuts. Bake for an additional 10 minutes.
Warm jam in a medium pot over medium heat. Add the cranberries and heat until well combined.
Preheat oven to 400 degrees F. Prepare a baking sheet with non-stick spray.
Lightly butter one side of each slice of bread. Place each buttered slice on the baking sheet, butter side up. Place in the preheated oven for 3-4 minutes, or until lightly toasted. Remove from the oven and flip bread slices.
On each bread slice, top with a smear of brie. Spoon about 1 Tbsp. of bacon and cranberry jam onto each crostini.
Place in the oven again for 4-5 minutes, or until brie is melted. Enjoy!