This recipe tastes alright, but it is needlessly complicated. My revised version is below. If you don't get that far, the takeaway is if you roast the brussels sprouts at 400 degrees for a total of 40 minutes as called for, you will get brussels ciders. Also, cut the amount of sprouts in half and leave everything else the same.
Cook bacon in a large skillet over medium, turning occasionally, until browned and crisp, about 10 minutes. Transfer to a plate lined with paper towels; reserve drippings in skillet.
Add shallots to hot drippings, and cook over medium, stirring often, until shallots are softened and start to brown, about 3 minutes. Add garlic, and cook, stirring often, 1 minute. Add vinegar, and cook until thick and syrupy, about 2 minutes. Remove from heat. Crumble bacon, and stir into shallot mixture. Cool to room temperature, cover, and chill until ready to use, up to 1 day ahead.
Preheat oven to 350°F. Toss Brussels sprouts with olive oil, 1 teaspoon of the salt, and 1/2 teaspoon of the pepper. Transfer to 1 aluminum foil-lined rimmed baking sheet. Roast Brussels sprouts in preheated oven until golden and tender, about 20 minutes, stirring halfway through baking. Set aside for up to 1 hour.
Add breadcrumbs and remaining 1/2 teaspoon salt and 1/4 teaspoon pepper to shallot/bacon mixture. Add butter if desired. Saute until breadcrumbs are lightly browned.
Add roasted Brussels sprouts to bacon-shallot mixture, and cook until heated through.