Cook linguine pasta according to package instructions.

Whisk together flour, chicken broth, milk, salt, and pepper in a bowl. Set aside.

Heat olive oil in a large skillet over medium-high heat.

Add sliced mushrooms to the skillet and sauté for 6 minutes.

Add minced garlic and sauté for 2 more minutes until garlic begins to brown.

Pour the flour, chicken broth, milk, salt, and pepper mixture into the skillet with mushrooms and garlic.

Bring to a simmer and cook, stirring occasionally, until thickened, about 3-4 minutes.

Add shredded Gruyere cheese and stir until the cheese has melted.

Mix in fresh baby spinach leaves and allow them to wilt.

Drain the cooked pasta and add it to the skillet.

Toss the pasta to coat it evenly with the sauce and serve immediately.