Cook the pasta in well-salted water according to package directions until just tender. Drain and set aside.

Melt the butter in a large skillet or Dutch oven over medium heat. Add the diced onion and cook until soft and lightly golden. Stir in the garlic and cook just until fragrant.

Slowly whisk in the chicken broth until smooth, then add the heavy cream and milk, stirring constantly.

Sprinkle the flour over the liquid mixture and whisk well until fully incorporated and smooth. Continue cooking and stirring for about one minute, allowing the sauce to thicken into a rich, velvety consistency.

Season with salt and black pepper. Add the chicken, peas, carrots, and corn. Stir until everything is warmed through and well coated in the sauce.

Add the cooked pasta and gently fold it into the sauce. Reduce the heat to low and let it simmer for a few minutes so the pasta absorbs the creaminess and the veggies are warmed through.

Remove from heat and garnish if desired. Serve warm.