Step 1: Prepare the Aromatics. In a food processor, pulse the quartered yellow onion until it forms a very fine paste, almost liquid, with no discernible chunks. Transfer the onion paste to a fine-mesh sieve and press out as much liquid as possible. This step is crucial for achieving the right texture.
Step 2: Combine Meats and Seasonings. In a large mixing bowl, combine the ground beef and ground lamb. Add the pressed onion paste, minced garlic, dried oregano, dried marjoram, dried thyme, garlic powder, onion powder, salt, black pepper, and the optional pinch of cayenne pepper.
Step 3: Mix Thoroughly. Using your hands, mix the ingredients together very thoroughly. Knead the meat mixture vigorously for at least 5-7 minutes. The goal is to develop the proteins, creating a very sticky and cohesive mixture that will yield the dense, uniform texture characteristic of gyro meat.
Step 4: Form the Loaf. Preheat your oven to 300°F (150°C). Line a standard 9x5 inch loaf pan with parchment paper, ensuring there's an overhang on the sides for easy removal. Firmly press the meat mixture into the loaf pan, making sure to eliminate any air pockets. Press down hard to compact the mixture as much as possible.
Step 5: Bake to Perfection. Place the loaf pan in a larger baking dish and carefully add about 1 inch of hot water to the larger dish to create a water bath. This helps the gyro meat cook gently and maintain moisture. Bake for 60-75 minutes, or until an instant-read thermometer inserted into the center of the loaf reads 165°F (74°C).
Step 6: Rest and Chill. Once cooked, carefully remove the loaf pan from the water bath and drain any accumulated fat. Place a heavy object (like another loaf pan filled with cans or heavy jars) on top of the cooked gyro meat loaf while it's still in the pan. This pressing step further compacts the meat. Allow it to cool completely to room temperature, then refrigerate for at least 4 hours, or preferably overnight. Chilling is essential for firming up the loaf, which makes slicing much easier.
Step 7: Slice and Sauté. Once thoroughly chilled, remove the gyro meat loaf from the pan using the parchment paper overhang. Use a very sharp knife or an electric carving knife to slice the loaf as thinly as possible – the thinner, the better! In a large skillet over medium-high heat, add 1 tablespoon of olive oil. Once hot, add the sliced gyro meat in a single layer. Cook for 2-3 minutes per side until beautifully browned and slightly crispy. Alternatively, you can broil the slices for 1-2 minutes per side for similar results.
Step 8: Serve and Enjoy. Serve your crispy, flavorful homemade gyro meat in warm pita bread with plenty of homemade tzatziki, fresh chopped tomatoes, thinly sliced red onion, and a sprinkle of fresh parsley. Enjoy your taste of Greece at home!