Preheat oven to 350°F.
Heat 4 tbsp oil in large sauté pan over medium-high heat. Cook Brussels sprouts in batches, cut-side down, without turning, until cut side is golden brown, 4–6 minutes. Season with ¼ tsp each salt and pepper while cooking.
Remove, and transfer to a bowl. (Sprouts will finish cooking in the oven, so no need to fully cook at this point)
Repeat with remaining batches, adding 2 tbsp olive oil or as needed to coat the Brussels while roasting. Set aside.
Meanwhile, heat the remaining 2 tbsp oil in a medium-size sauté pan over medium heat. Add bacon and cook, stirring occasionally, until crispy, 8–10 minutes. Transfer bacon to a plate, leaving fat in pan; set aside.
Reserve ¼ cup bacon fat; leave in pan.
Return pan to medium heat; add shallots and thyme. Cook, stirring often, until shallots are tender, 3–4 minutes. Add wine to pan; increase heat to high.
Cook, stirring often and scraping the bottom of the pan to incorporate bacon bits, until wine almost evaporates, 2–3 minutes.
Stir in cream, mustard, butter and thyme. Reduce heat to medium; stir in two-thirds of the cheese. Season with ½ tsp each salt and pepper. Stir in reserved bacon and Brussels sprouts. Transfer to a baking dish.
When ready to bake, toss breadcrumbs with reserved bacon fat. Season with salt and pepper. Distribute evenly over Brussels sprouts. Top with remaining cheese.
Bake until cream bubbles and breadcrumbs turn golden brown, 20–30 minutes. Serve hot.