Using an electric mixer, or a blender mix mascarpone with the sweetener and vanilla extract.
Take 1/2 of the mixture out of the blender or the mixing bowl and place it in another bowl. Add lemon zest and mix with a whisk.
In the remaining mixture, add in coffee and cacao powder. Blend or mix until it's unified.
In a dessert glass, first put some dark mixture, then the light one. Repeat this twice.
Blend the frozen berries and place them on top of your dessert. Decorate with a few whole berries.
Place the dessert in the freezer for 10 minutes and it's ready to be served. if you want to keep it for later, place the dessert in the refrigerator but cover each glass with some plastic foil.