Preheat your oven to 380°F. While it heats, remove the cream cheese from the refrigerator to soften to room temperature—this ensures it will blend smoothly into the turkey mixture without lumps. Shred the cheddar cheese fresh if you haven't already, as pre-shredded cheese contains anti-caking agents that can prevent smooth melting.

In a large skillet over medium-high heat, brown the ground turkey, breaking it into small pieces as it cooks for about 5-7 minutes until no pink remains. Pour off any excess fat through a fine mesh strainer or carefully tilt the pan—this step keeps the casserole from becoming greasy. I like to use Butterball turkey specifically because it's leaner to begin with, which means less fat to drain and a cleaner final dish.

Reduce heat to medium and add the softened cream cheese to the browned turkey, stirring constantly for 1-2 minutes until it melts and coats the meat evenly. Add the spinach and stir until completely wilted and incorporated, about 2-3 minutes. The cream cheese will coat everything and create a rich, creamy binding sauce.

Remove the skillet from heat and crack the egg directly into the mixture, stirring vigorously until fully incorporated. Add half of the shredded cheddar cheese, garlic powder, and salt, mixing thoroughly until everything is evenly distributed. The egg acts as a binder to help the casserole hold together when baked.

Pour the turkey mixture into a 9x9 inch baking dish (or similar size) and spread it evenly into an even layer. Season the top with black pepper to taste, then sprinkle the remaining half of the cheddar cheese over the top. I like to add a few cracks of fresh pepper right before baking because it won't lose its punch through the cooking process.

Bake for 20 minutes at 380°F until the top is golden and the cheese is melted and bubbly. The casserole will set as it cools slightly, so let it rest for 3-5 minutes before serving—this makes it easier to portion without falling apart.