Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper.
Slice the French baguette into ½-inch thick slices. Arrange the slices on the prepared baking sheet. Brush one side of each slice with olive oil.
Bake the baguette slices in the preheated oven for about 10-12 minutes, or until golden and crispy. Keep an eye on them to prevent burning. Once done, remove from the oven and set aside.
While the crostini are baking, prepare the balsamic roasted cranberries. In a small saucepan over medium heat, combine the fresh cranberries, balsamic vinegar, and brown sugar. Cook for about 10-15 minutes, stirring occasionally, until the cranberries have burst and the mixture has thickened. Remove from heat and let cool.
To assemble the crostini, place a slice of baked baguette on each serving plate. Top with a generous slice of creamy brie cheese followed by a spoonful of the balsamic roasted cranberries.
Optionally, sprinkle fresh thyme leaves over the assembled crostini for a pop of flavor and presentation.
Serve immediately while the crostini are still warm.