Bring a large pot of water to a boil.
In a deep skillet or large saucepan, heat the EVOO over medium-high. Add the bacon and cook until the fat melts, 2 to 3 minutes. Add the mushrooms, thyme and bay leaf. Cook until the mushrooms brown, 3 to 4 minutes. Add the ground beef and cook, breaking up into small pieces with a spoon, until browned, 4 to 5 minutes. Add the onion and garlic; season with salt and pepper.
Partially cover the skillet and cook, stirring occasionally, until the onion softens, 5 to 6 minutes. Add the tomato paste and stir until fragrant, about 1 minute. Stir in the stock, then reduce the heat to low and let the ragu simmer while the pasta cooks.
Salt the water and cook the pasta until al dente. Drain, reserving 1/2 cup of the pasta cooking water. Add the pasta and the cooking water back to the hot pot. Toss with half the ragu and the butter; season. Serve the pasta in shallow bowls topped with the remaining sauce and cheese.