Preheat the oven to 300°F. Line a baking sheet with parchment paper.
In a small bowl, whisk together the brown sugar and balsamic vinegar. Arrange the bacon in a single layer on the baking sheet. Brush the balsamic mixture atop the bacon.
Bake the bacon until partially cooked but still pliable, about 10 minutes. Remove the bacon from the oven and let it cool until it can be safely handled.
Divide the asparagus into six bundles. Wrap each bundle with one piece of bacon, starting about 1/2-inch from the top and wrapping down toward the stems. Arrange the bundles back on the baking sheet so that the end of the piece of the bacon is on the bottom of each bundle.
Increase the oven to 400°F. Roast the bundles until the asparagus is tender and the bacon is crispy, about 15 minutes, brushing the bacon with the balsamic mixture once halfway through. Remove the bundles from the oven and serve.