Pulse 1 cup farro in a blender until about half is broken into smaller pieces. Cook 1 chopped shallot and 1 chopped small fennel bulb in 2 tablespoons butter in a medium saucepan over medium-high heat, 5 minutes. Stir in the farro and 1 teaspoon kosher salt. Add 4 cups water; bring to a simmer. Cook until the farro is tender, 15 to 20 minutes. Stir in 1/4 cup grated parmesan and 2 tablespoons mascarpone; season with salt and pepper. Top with shaved parmesan and chopped fennel fronds.