Mousse: In a food processor, mix ricotta and lemon juice until very creamy and homogeneous.
In a bowl, whisk egg whites and tartar cream with a mixer until you have soft picks. Add sugar gradually while whisking until firm and straight picks, around 5 minutes. At low speed, incorporate the mixture of ricotta until all is homogeneous.
Raspberry Garnish: In a bowl, mix raspberries with jam.
Distribute the mousse in 4 parfait glass or ramequin (or any cute bowls you have) and add raspberry garnish. Put in the fridge. It's better if it's eaten the same day.