Whisk together apple cider vinegar, mustard, and maple syrup. Set aside.
Place bacon in a cold nonstick skillet. Cook over medium high heat until fat is rendered and bacon is crispy. Remove bacon from pan with a slotted spoon and set aside.
You should have about 3 tablespoons of bacon fat left in the pan. Add enough olive oil to the pan to have 4 tablespoons (1/4 cup) fat total.
Add shallots to the pan and cook until softened, about 3 minutes. Slowly and carefully add apple cider vinegar mixture, whisking to combine. Season with 1/4 teaspoon freshly-ground black pepper. Simmer for about 2 minutes, just until the dressing coats the back of a spoon.
Add about half of the reserved bacon back into the dressing, saving the rest to sprinkle over the salad. Let the dressing cool until just warm and season to taste with salt and pepper.
In a large bowl, toss together frisee, sliced pears, about half of the dressing, and pecans. Season to taste with salt and pepper.
Serve immediately, topped with crumbled blue cheese, an extra drizzling of dressing, and the remaining crumbled bacon, if desired.
To prevent sliced pears from browning, dip them in a mixture of 50% water: 50% lemon juice.