Add the bacon and cook, stirring occasionally, until browned and crispy, about 4 minutes.
Remove the bacon to a paper-towel-lined plate and set aside. Discard all but 3 tablespoons of the fat.
Place the pan with the remaining bacon fat over medium heat, add the shallot, and cook until fragrant, about 30 seconds.
Whisk in the vinegar, brown sugar, and Dijon mustard; remove from heat and season with salt and pepper.
Combine the spinach, reserved bacon, and pecans in a large bowl.
Add the vinaigrette and toss to coat. Season with additional salt and pepper and serve immediately.Beverage pairing: Niklas Sauvignon Blanc, Alto Adige, Italy. This dish is rich with bacon fat and tart with vinegar, so a high-acid wine is needed to stand up to both. This bright Sauvignon from the northern reaches of Italy’s Alto Adige has the tartness and pungency to balance the dish.