In a bowl, whisk together sugar, vinegar, and a generous pinch of salt and pepper. About 15 minutes before serving, add the strawberries and toss gently until they are well coated.
Gently crush 1 biscotti into each of 4 serving bowls. Top with the marinated strawberries, dividing them evenly. Put a dollop of mascarpone cheese on each serving and serve immediately.
Makes: 4