In a small saucepan, bring vinegar to a boil over medium heat. Reduce heat, and simmer until vinegar is reduced by half, about 15 minutes. Transfer to a heatproof bowl, and let cool completely.
Preheat oven to 400°. Line 2 rimmed baking sheets with parchment paper.
Using a serrated knife in a gentle sawing motion, cut baguette into ⅛-inch-thick slices. Place on prepared pans, and drizzle with oil.
Bake until crisp, about 15 minutes. Let cool slightly.
In a small bowl, stir together mascarpone and pepper. Spread mascarpone mixture onto crostini. Top with strawberries, and drizzle with balsamic reduction. Serve immediately.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/strawberry-balsamic-bites-recipe/