Begin cooking pasta according to package instructions.
Whisk together flour, chicken broth, milk, salt, and pepper. Set aside.
While pasta cooks, in a large skillet heat olive oil over medium-high heat. When oil begins to ripple add sliced mushrooms, sauté for 6 minutes. Add minced garlic, sauté for 2 more minutes until garlic just begins to brown.
Whisk flour, chicken broth, milk, salt and pepper mixture into mushrooms and garlic, bring to a simmer and cook, stirring occasionally until thickened, about 3-4 minutes.