Crisp bacon in a heavy-bottomed skillet over medium heat, stirring occasionally. Remove bacon with a slotted spoon and drain on paper towel.
Remove (and reserve) all but 2 tablespoons of the rendered fat from the pan and arrange Brussels sprouts in a single layer, cut side down. Season with salt, cover and cook for 5 minutes. Increase heat to medium-high and continue to cook uncovered until tender, another 3–5 minutes.
Remove Brussels sprouts to a warmed serving bowl and toss with bacon.
Add an additional tablespoon of fat to pan, add shallot and stir, allowing to soften.
Add cider vinegar and cook a minute more, swirling to combine with the remaining fat in the pan.
Remove pan from heat, add thyme, season with salt and pepper and pour vinaigrette over the Brussels sprouts, tossing to coat.
Yield: about 3 cups.