Place the strawberries in a bowl.
In a small bowl, whisk together the vinegar, sugar, salt and pepper. Let stand for 15 minutes, stirring occasionally to completely dissolve the sugar.
Pour the marinade over the berries and gently toss to coat.
Divide the biscotti pieces into 4 bowls. Spoon the berries and some of the marinade over each and top with a dollop of marscarpone. Serve immediately.