Merry Berry Filling (continuation for Mrs. Billet's cake)

1 cup fresh cranberries (frozen or dried will work as well)
1 cup fresh raspberries
1/2 cup sugar
3 tbsp. water
2 tbsp. cornstartch
1 tbsp. cold water
1 cup chopped fresh stawberries
2 tbsp. butter

1. Cook first 4 ingredients in a medium saucepan over medium-low heat for 3-4 minutes or until cranberries start to pop. Stir often.
2. Whisk together cornstarch and 1 tbsp. cold water until smooth; add to cranberry mixture. Cook, stirring constantly for 1 minute.
3. Stir in strawberries and butter until butter is melted.
4. Cool to room temperature (about 30 minutes). Cover and chill for 6 hours.