Preheat oven to 350 degrees. Do not grease the pan. Wrap chestnuts with half pieces of bacon and secure with a toothpick. (top) Bake in the oven for aprox. 30 minutes covered with aluminum foil.
Pull out and drain the grease gently by tilting the pan. Pour the mixture of brown sugar and ketchup over water chestnuts. Make sure to coat them. Bake uncovered for another 30 minutes or if they seem to be getting too dark; pull out. Enjoy!