Remove stems from strawberries and cut in half. In a medium bowl, toss strawberries with sugar, balsamic vinegar and black pepper to coat. Add thyme sprig. Refrigerate for up to 8 hours or let sit at room temperature for 30 minutes.
Heat oven to 400°. Place strawberry mixture onto a parchment-lined rimmed baking sheet. Bake for about 30 minutes. Cool. Remove thyme sprig.