In a medium sauté pan, add about 2 tablespoons of olive oil and begin cooking onion and garlic over medium low heat, stirring frequently. Cook until they are mostly translucent then add the ground chicken, thyme, rosemary, parsley, a few cracks of fresh black pepper and 1 teaspoon kosher salt.

Increase the heat to medium and cook until the chicken is almost fully cooked.

Add the Worcestershire sauce and tomato paste, stirring to coat. Then sprinkle on the flour and stir to incorporate. Add the chicken stock and frozen vegetables and continue cooking, stirring frequently until the sauce has thickened and reduced to the point of holding a line when you run your spatula or spoon through the bottom.

Once you add the chicken stock and vegetables to the filling, place the potatoes in a large saucepan and add enough cold water just to cover. [This can, of course, be done right after peeling to keep them from browning.] Cook over high heat until the potatoes are tender and can easily be pierced with a fork or cake tester.

Strain the potatoes and transfer to the bowl of a stand mixer with the paddle attachment or back to the cooking pot. If using a potato masher, and the butter, salt, garlic powder and mash until the butter melts. Add the milk a bit at a time until you have a thick but spreadable consistency. If using a stand mixer, break up the potatoes on medium speed then reduce to low and add the butter and seasoning. Mix until melted, then begin adding the milk slowly until the spreadable consistency is reached.

Once the filling mixture has thickened either set it aside or transfer to a 9 x 9 -inch baking dish. I cooked the filling and baked the final dish in a 2 ¼ quart Le Creuset cast iron braiser. Super easy.

Dollop and spread the mashed potatoes evenly over the top of the filling. Pay special attention to sealing the edges. This will keep the filling from bubbling up over top of your topping. I made some nice swirls and such, but you could also pipe it for a fancier presentation.

For preparing ahead: You can cool, cover and refrigerate the prepared dish prior to baking for up to 3 days. It will affect the potato texture but is a super great way to meal prep. You can also freeze the dish at this stage for several months. The potatoes will also be less smooth than when baked fresh. When you are ready, preheat the oven to 400°F and bake as directed.