Blanch asparagus in a large pot of salted boiling water for 1 minute. Drain and transfer to an ice bath. In a small bowl, combine the maple syrup, Dijon mustard, balsamic vinegar, salt and pepper. In a large skillet, melt butter over medium heat, add shallots and garlic, and sauté for 1 minute. Add the asparagus and Dijon maple sauce and sauté until asparagus is coated, about 1 minute.