For the mascarpone sorbetto: Combine the sugar and 1 1/4 cups water in a small saucepan. Place over medium-low heat and bring to a simmer, stirring occasionally with a rubber spatula to dissolve the sugar. Simmer for 1 minute. Remove from the heat and add the lemon zest, lemon juice and salt. Set aside to cool slightly.
In a medium bowl, whisk the mascarpone to soften. Add the lemon syrup and whisk until smooth. Allow to cool completely to room temperature, about 30 minutes.
Prepare your ice cream maker. Whisk the mascarpone mixture one more time to incorporate, and then freeze according to manufacturer's instructions. Transfer the sorbetto to the freezer to freeze completely.
For the rosemary honey: Meanwhile, place the honey, rosemary and 2 tablespoons water in a small skillet. Bring to a simmer over low heat and simmer gently for about 5 minutes. Strain through a fine-mesh strainer and cool to room temperature.
To serve, scoop the sorbetto into coupe glasses and drizzle with the desired amount of rosemary honey.