Preheat a large cast-iron pan to medium low heat. Add the avocado oil and butter to the pan, followed by the sliced onions, garlic and thyme. Season the onions with a pinch of salt and pepper and cook for 35-40 minutes, stirring every 5 minutes, to prevent the onions from sticking to the pan.

Once the onions are golden brown and evenly caramelized, scoop them out from the pan and set aside. Place the pan back on the element and raise the heat to medium-high. Add the ground turkey to the pan and use a spoon to break the turkey up into small pieces. Season with sea salt, black pepper, poultry seasoning, nutmeg and Worcestershire sauce. Cook, stirring often, for 8-10 minutes, until no pink remains. Once the turkey has fully cooked, remove the pan from the heat and set aside.

Unroll the puff pastry sheets and use a sharp knife to cut each sheet into 16 equal squares. Line two cookie sheets with parchment paper and place the puff pastry squares onto the pan, making sure they are evenly spaced out.

Use a spatula to spread about ½ tsp of the mascarpone cheese in the middle of each puff pastry square, leaving an even border on all sides of the square.

Next, spoon about 1 tsp of the caramelized onion mixture on top of the cheese, followed by 1 tsp of the ground turkey mixture on each of the puff pastry squares. Use a pastry brush to brush the egg onto the exposed puff pastry edges.

Place the cookie sheets into the oven for 22-25 minutes, or until the puff pastry is golden brown. Remove from the oven and let cool for about 5 minutes. Just before serving, sprinkle a few pomegranate arils onto each tartlet.