Boil orecchiette in a large pot of salted water until al dente, according to package instructions. Reserve about 1/2 cup of pasta water, then drain the rest and set the pasta aside.

Heat a large skillet over medium heat and cook the chopped bacon until crisp. Remove it with a slotted spoon and transfer to a paper towel-lined plate. Leave about 2 teaspoons of bacon grease in the skillet for added flavor.

Melt butter in the skillet with the bacon grease over medium heat. Add the sliced mushrooms in a single layer and cook undisturbed for 3–4 minutes to develop a golden-brown crust. Stir and sauté for another 3 minutes until tender. Add minced garlic and cook for 1 minute, infusing the mushrooms with aromatic depth.

Whisk cornstarch with half-and-half in a mixing bowl until smooth. Pour this mixture into the skillet, followed by the milk, Parmesan cheese, thyme, salt, and pepper. Stir everything together and simmer gently for 5 minutes, allowing the sauce to thicken and the flavors to meld.

Add the cooked orecchiette and crumbled bacon to the skillet. Use tongs to toss everything together, ensuring the pasta is coated evenly with the luscious sauce. Adjust the thickness of the sauce with the reserved pasta water if needed. Garnish with more Parmesan and thyme for a finishing touch.