1. To blanch Brussel sprouts: Prepare a large bowl of ice water and set aside. Bring a large pot of water to a rolling boil over high heat. Generously season water with salt. Add Brussel sprouts and cook until crisp-tender, about 5 minutes. Remove Brussel sprouts from boiling water and transfer to a bowl of ice water; cool and drain well.

2. To render bacon: To a large skillet set over medium-high heat, add oil. When oil is shimmering, add bacon and cook until crispy, about 6 minutes. Using a slotted spoon, transfer bacon to a paper towel-lined plate. Reserve bacon fat.

3. To pan-roast Brussels sprouts: Add Brussels sprouts to skillet with bacon fat, cut side down and cook, stirring occasionally until sprouts are browned, about 5 minutes. Remove skillet from heat and add mustard and vinegar; toss until well combined. Add thyme, lemon zest, walnuts and bacon; stir to combine. Taste and adjust seasoning with salt and pepper.

4. To serve: Transfer Brussels sprouts to a medium platter or bowl and serve immediately.