Use a sharp knife to cut the chicken into cubes. Then, in a large pot, melt the butter and brown the cubes of chicken on all sides. Cook for 5-8 minutes.
Add the garlic and sauté with the chicken for 2 minutes, then pour in the penne pasta and the chicken stock. Cover and cook on low for 8 minutes. Stir the pot occasionally to make sure the pasta doesn’t stick to the bottom.
Once the pasta is partly cooked, add in the whole milk, cream cheese, half the Parmesan cheese, pesto, sundried tomatoes, and salt and pepper. Give it a good stir to mix the cream cheese throughout the dish, then cover and simmer for another 5 minutes.
When the sauce has thickened, and the pasta is cooked to your liking, sprinkle on the rest of the parmesan and serve.