Add 1 ½ Tbsp salt in 4 quarts (4L) of water and bring it to a boil for cooking spaghetti. Meanwhile, prepare the rest of the ingredients. Once water is boiling, add spaghetti and cook according to package instructions. Tip 1: Stop cooking 1 minute earlier as you will continue to cook pasta in the frying pan. Tip 2: Before draining the pasta, reserve ½ cup (120 ml) pasta cooking water. Drain well and set aside.
Cut the bacon slices into ½ inch (1.25 cm) pieces.
Cut the bottom of the mushrooms and slice them. Cut the bottom end of shimeji mushrooms.
Remove the stem of shiitake mushrooms and slice them.
In a large frying pan, heat 1 ½ Tbsp olive oil on medium heat. Note: if you use a non-stick frying pan, you can skip the oil.
Once the oil is hot, add the bacon and sauté.
Once the bacon fat renders, crush 2 cloves garlic and add into the pan.
Add all the mushrooms and saute together. Add 1 Tbsp butter and freshly ground black pepper.
Add the flour and make sure to keep stirring so the flour doesn’t stick at the bottom of the pan.
Stir in 1 cup milk, ⅓ cup heavy cream, and 1 Tbsp soy sauce. Continue scraping off the bottom of the pan. Flour will thicken the sauce.
Taste the sauce and add salt and freshly ground black pepper to taste if necessary. If the sauce is too thick, you can add ¼ cup of pasta cooking water (after that, add a tablespoon one at a time) to dilute the sauce. Tip: You want to make sure it tastes a bit stronger than you want the final dish to be (because you will add spaghetti).
Add cooked spaghetti in the frying pan, or alternatively, you can pour the sauce over the spaghetti on a serving plate. Using the pair of tongs, coat the spaghetti with the sauce.
If you like, add freshly ground black pepper. Serve and garnish with parsley.