Place mixing bowl and beaters in the freezer to chill.

Wash and prepare fresh berries.

Combine berries and 1 cup of sugar in a medium saucepan.

Cook over medium heat, mashing and stirring occasionally until the berries soften and release their juices.

Dissolve cornstarch in cold water.

Add the dissolved cornstarch to the berry mixture.

Continue cooking until the mixture thickens and becomes transparent.

Remove from heat and let cool completely.

Remove the chilled bowl and beaters from the freezer.

Combine egg whites and 3/4 cup of sugar in the chilled bowl.

Beat on high speed with an electric mixer until soft peaks form.

Gently fold the cooled berry mixture into the meringue.

Mix on low speed until just blended.

Pour the mixture over individual cake slices to serve immediately.