1. In a small saucepan over medium heat, combine the raspberries, sugar, and lemon juice. Stir occasionally until the raspberries break down and the mixture thickens, about 5-7 minutes.
2. Pass the raspberry mixture through a fine-mesh sieve to remove the seeds, and let it cool to room temperature.
3. In a large mixing bowl, beat the mascarpone cheese until smooth. Gradually add the cooled raspberry puree, mixing until well combined.
4. In a separate bowl, whip the heavy cream with vanilla extract and a pinch of salt until soft peaks form.
5. Gently fold the whipped cream into the raspberry-mascarpone mixture until fully incorporated. Be careful not to deflate the cream.
6. Spoon the mousse into individual serving glasses and refrigerate for at least 2 hours, allowing the flavors to meld and the mousse to set.

And there you have it, a dessert that not only tastes heavenly but also brings a piece of my cherished childhood to your table.