Brown bacon in cooking oil and then set aside both the bacon and oil.
In a deep pan, sauté garlic and onion in butter until tender. Add the mushrooms and cook until a bit brown. Add milk and cream and let cook until thick stirring constantly. Add bacon with the oil. Add parmesan cheese and salt and pepper. Remove from heat.
Pour into cooked noodles of your choice and mix. You may add more parmesan cheese on top and freshly grated pepper before serving.
Notes
When seasoning the sauce with salt, take into consideration the pasta that will be added later on. When you think it has the already the desired saltiness, just add a bit more salt (¼ - ½ teaspoon) to the sauce to avoid bland tasting carbonara.