Prepare the Brussels sprouts by cutting off the base and cutting in half lengthwise. Puree the orange juice, shallot, olive oil, vinegar, mustard, maple syrup, and salt in a food processor. Taste for seasoning; set aside. In a 12-inch skillet, fry the bacon until crispy, drain on a paper towel, and chop; set aside.
In a small bowl lined with foil, drain the bacon grease, except for 2 Tbsp. Turn the heat to medium-high, add the Brussels sprouts, cut side down, until browned; about 5 minutes. (If your pan is smaller, do this in two batches with more bacon grease the second time).
Add the pureed maple-orange mixture to the pan and gently stir the Brussels sprouts to coat with the mixture. Continue cooking for about 2 minutes, stirring, until caramelized. Season with salt and freshly ground black pepper to taste. Remove from heat and toss with the chopped bacon. Garnish with shaved or grated Parmesan.