Whisk together the sugar, water, and salt in a small saucepan set over medium heat. Bring to a boil and then reduce to a simmer. Cook for 5 minutes or until the sugar is completely dissolved in the water.
Add in the strawberries. Peel the lemons and add in the lemon peel (set aside the peeled lemons for later). Simmer for a few minutes and then remove the pan from the heat.
Allow the syrup to cool completely to room temperature, which will allow the strawberry and lemon flavors to fully infuse.
Once the syrup is cooled, squeeze in the juice of the peeled lemons and then add the entire mixture to a blender. Blend on high until everything is completely smooth and pureed.
Pass the syrup through a fine-mesh strainer set over a large bowl. Discard the solids.
Stir the softened mascarpone cheese into the strawberry lemon syrup until smooth and creamy. Chill the mixture in the fridge for at least 2 hours.
Churn the chilled mixture in an ice cream maker, according to the manufacturer’s instructions. Transfer the churned sorbet to an airtight container and chill in the freezer for at least 2 hours before scooping and serving.