Combine crushed fresh berries and sugar in a saucepan.

Cook over low heat, stirring constantly until the mixture thickens and becomes glossy.

If using a microwave, stir berries and sugar in a microwave-safe bowl and microwave on low power, checking and stirring frequently until thickened.

Stir in lemon juice.

Transfer the filling to a small container.

Allow the filling to cool to room temperature.

Seal the container tightly.

Chill the filled container in the refrigerator for at least 30 minutes.

The filling will keep in the refrigerator for up to 1 week.