Follow these detailed steps to craft your masterpiece. The process involves preparing the bread coffin, mixing the dip, and then baking it all to golden, bubbly perfection.

Step 1: Prepare the Pumpernickel Coffin

1. Preheat Your Oven: Begin by preheating your oven to 350°F (175°C). This ensures it’s ready for toasting the bread pieces and baking the dip.
2. Carve the Coffin: Place the rectangular pumpernickel loaf on a large cutting board. Using a sharp serrated bread knife, carefully cut a rectangle into the top of the loaf, leaving about a 1-inch border around the edges. Do not cut all the way through; cut down about 2-3 inches deep.
3. Create the Lid: Gently pry the cut rectangular section out of the loaf. This piece will serve as the “coffin lid.” Set it aside.
4. Hollow Out the Loaf: Reach into the hollowed-out section of the loaf and carefully pull out the soft bread from the inside, leaving a sturdy wall about 1-inch thick on all sides and on the bottom. Be careful not to puncture the bottom or sides. This hollowed loaf is your “coffin.”
5. Prepare the Bread for Toasting: Tear the removed bread interior and the “coffin lid” into bite-sized pieces, perfect for dipping. Place these pieces, along with the hollowed-out coffin, onto a large baking sheet.
6. Toast the Bread: Drizzle the bread pieces and the inside of the coffin with olive oil. Sprinkle the bite-sized pieces with garlic powder and a pinch of salt. Bake for 10-12 minutes, or until the pieces are lightly toasted and crispy. Remove the toasted pieces from the baking sheet and set them aside. Leave the coffin on the sheet.

Step 2: Create the Spinach Dip Filling

1. Prepare the Spinach: While the bread is toasting, prepare your spinach. Place the thawed spinach in the center of a clean kitchen towel or several layers of heavy-duty paper towels. Gather the towel around the spinach and wring it out with all your might over a sink. You will be amazed at how much water comes out. This step is absolutely critical to prevent a soggy dip. The spinach should be a compact, dry ball when you’re finished.
2. Sauté Aromatics (Optional but Recommended): In a small skillet, heat a teaspoon of olive oil over medium heat. Add the finely chopped onion and sauté for 3-4 minutes until softened and translucent. Add the minced garlic and cook for another minute until fragrant. This step deepens the flavor of the dip.
3. Combine the Wet Ingredients: In a large mixing bowl, combine the softened cream cheese, sour cream, and mayonnaise. Use a hand mixer or a strong spatula to beat the ingredients together until they are completely smooth and no lumps of cream cheese remain.
4. Add Cheeses and Seasonings: To the creamy base, add the grated Parmesan cheese, shredded mozzarella (reserving about 1/4 cup for the topping), salt, pepper, and optional red pepper flakes. Mix until well combined.
5. Fold in the Solids: Add the squeezed-dry spinach, chopped artichoke hearts, and the sautéed onion and garlic mixture to the cheese base. Use a spatula to fold everything together until all the ingredients are evenly distributed throughout the dip.

Step 3: Assemble and Bake

1. Fill the Coffin: Carefully spoon the prepared spinach dip mixture into the hollowed-out pumpernickel coffin on the baking sheet. Fill it all the way to the top, mounding it slightly in the center.
2. Top with Cheese: Sprinkle the reserved 1/4 cup of shredded mozzarella cheese over the top of the dip.
3. Bake to Perfection: Place the baking sheet with the filled coffin back into the 350°F (175°C) oven. Bake for 25-30 minutes. The dip is ready when it is heated through, bubbly around the edges, and the cheese on top is melted and lightly golden brown.
4. Final Touches: For a more browned, spooky top, you can switch the oven to the broiler setting for the last 1-2 minutes of cooking. Watch it very carefully, as it can go from golden to burnt in seconds.
5. Rest and Serve: Carefully remove the coffin dip from the oven and let it rest for 5-10 minutes before serving. This allows the dip to set slightly, making it less runny.