Heat oven to 400°F. Grease a 2-quart baking dish or oven-safe skillet.
Parboil sliced potatoes in salted water until just tender, 8–10 minutes. Drain and let steam-dry.
Cook bacon in a large skillet over medium heat until browned, 6–8 minutes. Transfer to a plate.
Melt butter with olive oil in the same skillet. Soften onions with thyme and a pinch of salt, 8–10 minutes.
Stir in garlic for 30 seconds. Pour in white wine, scraping up browned bits. Simmer until nearly evaporated.
Toss warm potatoes with crème fraîche, salt, and pepper. Fold in half the bacon-onion mixture.
Layer half the potato mixture in the dish. Add half the remaining bacon-onions and half the cheese. Repeat layers.
Bake until bubbling and golden, 20–25 minutes. Broil 1–2 minutes if needed. Rest 10 minutes before serving.