Add the raspberries, sweetener, and lemon juice to a saucepan. Cook over medium heat until the berries soften and the mixture begins to thicken. Set aside to cool, and strain out the seeds if you prefer a smoother layer.

Melt the white chocolate chips in a microwave-safe bowl, heating in short intervals and stirring until smooth. Let it cool for a moment.

In a separate bowl, whip the heavy cream with the vanilla and sweetener (if using) until stiff peaks form.

Gently fold the melted white chocolate into the whipped cream until the mixture is light and fully combined.

Add a spoonful of raspberry sauce to the bottom of each serving glass.

Carefully spoon or pipe the mousse over the raspberry layer.

If your glasses are tall, repeat the layers.

Chill for at least 30 minutes to set.

Top with a fresh raspberry or a few white chocolate shavings just before serving.