- Process raspberries and strawberries in batches in a food processor or blender until smooth.
- Transfer to a food mill or push through a fine sieve into a large measuring cup or bowl.
- Add enough water to the strained berries to equal 5 cups liquid.
- Whisk cornstarch and water in a small bowl. Whisk the cornstarch mixture and granulated sugar into the strained berries and transfer to a Dutch oven or large saucepan.
- Cook over medium heat, whisking constantly (make sure to whisk the bottom well), until the mixture is very hot and beginning to bubble.
- Cook for 1 minute more, whisking constantly.
- Transfer the pudding to a large bowl and let cool for 10 minutes.
- Press a piece of plastic wrap directly onto the surface and chill in the refrigerator for at least 2 hours (it will continue to thicken as it chills).
- Whip cream in a small bowl until soft peaks form.
- Add confectioners’ sugar and vanilla; continue whipping until firm peaks form. Fold in yogurt.
- Serve the pudding with a dollop of cream on top.