Preheat your oven to 350°F (175°C).

In a mixing bowl, combine the condensed cream of chicken soup with half a cup of whole milk. Add garlic powder, onion powder, dried rosemary, dried thyme, kosher salt, and freshly ground pepper. Whisk until smooth.

Spread the shredded cooked chicken in the bottom of a 9x13 inch baking dish.

Spoon the prepared mashed potatoes over the shredded chicken, smoothing them out evenly.

Pour the gravy mixture evenly over the mashed potatoes.

Sprinkle a generous amount of grated sharp cheddar cheese on top, if desired.

Bake for approximately 30 minutes until the top is golden brown and bubbly.

Let the casserole sit for a few minutes before serving.