In a small saucepan, combine the cranberries and water, cover, and place over medium heat. Cook until the cranberries pop and the liquid bubbles. Pass the cranberries through a strainer, pressing well with a spoon. Be sure to scrape all the lovely red puree on the underside of the strainer into the bowl to use. Pour the cranberry puree back into the saucepan and set aside. Let it cool a tad.
Whisk together the egg yolks and egg until combined. While whisking, pour in sugar and whisk until a light yellow color. Add the egg mixture to the cranberry puree in the sauce pan, and continue whisking until creamy and well incorporated, about one minute. Place over medium heat, whisking constantly, until the custard thickens and can coat the back of a wooden spoon, about 8-10 minutes. Remove the pan from the heat, and stir in the butter, one cube at a time. Strain into a bowl or jar, cover surface with plastic wrap and chill in the refrigerator for at least one hour.
Adapted from my Lemon Curd and Food.com's Cranberry Curd.How to Store Cranberry Curd
While fruit curds may not have the acidity necessary for long-term canning shelf-life, you can store the cranberry curd tightly covered in the refrigerator for one week or longer in the freezer. To defrost, let it thaw in the refrigerator before serving.