Preparation Preheat oven to 400°F. Place potatoes in a medium pot, pour in cold water to cover, and season with salt. Bring to a boil; reduce heat to low and cook until potatoes are fork-tender, 20–25 minutes. Drain and return potatoes to pot; add 2 Tbsp. butter. Meanwhile, trim very base of cabbage, then pull off outer leaves, being careful not to tear them, until you have 10 total. Cut out any tough ribs; discard. Cook leaves in a large pot of boiling salted water until tender, about 8 minutes. Transfer to a bowl of ice water and let cool. Transfer to clean kitchen towels and pat dry. Thinly slice remaining cabbage. Cook bacon in a 10"-diameter ovenproof skillet, preferably cast-iron, over medium, stirring occasionally, until bacon is beginning to crisp, about 6 minutes. Add sliced cabbage and onion and cook, stirring occasionally, until tender and starting to caramelize (vegetables will be golden brown), 20–25 minutes. Add vinegar, scraping up browned bits, then mix in thyme, pepper, and ½ tsp. salt. Remove from heat. Mash potatoes with a potato masher until soft. Whisk eggs and cream in a small bowl, then add to potatoes and mash to combine. Add bacon mixture, cheese, and ½ tsp. salt and mix well. Taste and add more salt if needed. Wipe out and reserve skillet. Break up 1 Tbsp. butter into smaller pieces and dot around reserved skillet. Line with a single layer of cabbage leaves, overlapping slightly and allowing them to hang over edges of skillet. Scrape in potato mixture and spread out to the edges, flattening out evenly with a rubber spatula. Fold overhanging leaves up and over filling and top with more cabbage leaves, overlapping them slightly to create a single layer. Break up remaining 1 Tbsp. butter and dot over top. Roast cabbage pie until lightly browned, 30–35 minutes. Let cool 10 minutes before cutting into wedges.