Preheat oven to 450°F.

Pat the chicken dry and season with salt and pepper. Add 3 cups of chicken broth to a medium saucepan and add the chicken. Gradually bring it to a gentle boil. Let the chicken cook with the lid cracked for 15 minutes, or until cooked through. Don't boil rapidly or the chicken will be tough. Remove the chicken and use forks to shred. Set aside and reserve the broth that the chicken cooked in.

While the chicken cooks, melt 4 tablespoons butter in a wide 12-inch pan over medium heat. Add the onions and sauté them for 4 minutes. Add the garlic and seasonings. Toss to coat and cook for 1 more minute.

Add the flour and toss to coat. Cook for 2 minutes or until you can no longer smell raw flour.

Reduce heat to low. Add 2 cups of the reserved chicken broth in small splashes, stirring to incorporate. Add the half and half in the same manner. Adding the liquid too quickly will break the roux and interfere with the thickness of the gravy.

Add chicken bouillon and 1 teaspoon Worcestershire sauce. Then add the shredded chicken and stir to combine.

Increase heat to medium and continue to add splashes of the remaining 1 cup of chicken broth while letting the filling simmer, reduce, and concentrate for 10-15 minutes. Use about 3/4 of the remaining cup.

Add the frozen vegetables and stir to combine and heat through. Remove from heat.

Transfer filling to a lightly greased 9x13-inch baking dish if your skillet isn't oven/broil safe.

Let the filling cool slightly, then carefully place scoops of warm potatoes on the top. Try to add several scoops that are all almost touching each other to eliminate the amount of spreading you'll need to do.

Use a silicone spatula to gently spread the warm potatoes in an even and smooth layer over the filling. Don't push down hard to ensure the potatoes stay on the top.

If desired, use a fork to rake a design on the top. Place in the preheated oven and bake uncovered for 10 minutes.

Set broiler to high (550°F), and let the top brown for about 4 minutes, watch it carefully during this time to ensure it doesn't burn. Don't do this with glass or Pyrex baking dishes.

Remove and garnish with parsley. Let it sit for 5 minutes prior to serving.