In a saucepan, muddle the sugar and rosemary leaves. Stir in 3 cups water and cook over medium heat just until the sugar dissolves. Transfer the mixture to a large bowl and let cool to room temperature. Add the pears and let sit for 30 minutes.
Meanwhile, grease a grill or grill pan and preheat to medium. In a large bowl, whip the cream until soft peaks form. Fold the mascarpone into the whipped cream; refrigerate.
Drain the pears and pat with paper towels. Add the pears cut side down to the hot grill or grill pan and cook until tender and grill marks appear, about 10 minutes. Season with pepper. To serve, top with the mascarpone cream and almonds.