Heat 1⁄2 tablespoon of the oil in a large cast-iron skillet or sauté pan over medium-high heat. Combine the beef and flour in a bowl, season with salt and pepper, and toss to lightly coat the beef. Working in two batches to avoid crowding the pan, sear the beef in the hot oil, turning occasionally, until nicely browned. Transfer to a slow cooker. Add the remaining oil to the skillet. Add the chopped onions and cook for about 5 minutes, until lightly browned. Stir in the wine and tomato paste, scraping the bottom of the pan to free up any browned bits. Pour the onion mixture over the beef, then add the broth, bay leaves, and thyme. Set the slow cooker to high, cover, and cook for about 4 hours (or on low for 8 hours), until the beef is fork-tender. An hour before serving, add the potatoes, carrots, and pearl onions. Five minutes before serving, add the peas. Discard the bay leaves and thyme branches and season with salt and black pepper. Serve garnished with parsley or gremolata if you like.