Place the stock in a sauce pot and warm it over medium heat then reduce to simmer.
Heat the extra-virgin olive oil and the butter in a large, deep skillet over medium to medium-high heat. Add the bacon to brown. Next add the garlic and spaghetti and toast the noodles lightly, 3 to 4 minutes.
Add onions and mushrooms, thyme and season with salt and pepper. Soften veggies a bit, 5 minutes. Add a few ladles of stock and stir the pasta. Keep stirring adding stock a few ladles at a time allowing liquids to be mostly absorbed before adding more, as if you were preparing a risotto. When liquids are absorbed and spaghetti is cooked to al dente, 12-15 minutes, stir in cheese.
Adjust salt and pepper. Turn off heat and stir another minute. Remove the thyme stems. Serve in shallow bowls and garnish with lots of parsley