Preheat an oven to 350 degrees F (175 degrees C). Place 6 custard cups in a 9x13-inch baking dish. Bring a kettle of water to the boil. Combine the brown sugar, pumpkin pie spice, cayenne pepper, vanilla extract, orange juice, and lightly beaten egg whites in a mixing bowl. Stir in the pumpkin and evaporated milk until well blended. Carefully ladle the custard into each cup, dividing the mixture evenly. Pour boiling water around the cups to a depth of at least 1 inch. Bake the custards in the preheated oven until a knife inserted into the center of the custard comes out clean, about 45 minutes. Carefully remove the pan from the oven; allow to cool. Remove the custard cups from the water bath and cool completely on a wire rack. Refrigerate before serving. Serve garnished with a tablespoon of real whipped cream, if desired.