Step 1

In a large bowl, whisk together the flour, salt, sugar, and instant yeast. In a medium bowl, combine the milk, water, 4 tablespoons melted butter, and vanilla. Stir to combine, then add to the flour. Using a rubber spatula, mix until the liquid is absorbed and the ingredients form a sticky dough ball. Cover the bowl with a damp tea towel or plastic wrap and set aside in a warm spot to rise for 1½ to 2 hours, until the dough has doubled in bulk.

Step 2

Set a rack in the middle of the oven and preheat it to 375°F. Grease a panettone mold (see Note) with the softened butter—be generous. Sprinkle the chocolate pieces over the surface of the dough. Using two forks, deflate the dough by releasing it from the sides of the bowl and pulling it toward the center. Rotate the bowl quarter turns as you deflate, turning the mass into a rough ball. Keep turning the dough in this manner until the chocolate is incorporated.

Step 3

Use your two forks to transfer the dough to the prepared mold. If the dough is too wet to transfer with forks, lightly grease your hands with butter or oil, then transfer it to the mold. Do not cover the mold. Let the dough rise on the countertop near the oven (or another warm, draft-free spot) for 20 to 25 minutes, until the dough has doubled in bulk—it may not crown the rim, but it will come close.

Step 4

Set the mold on a sheet pan and transfer it to the oven. Bake the mold for 40 to 45 minutes, or until uniformly brown. Remove the pan and mold from the oven and set the mold onto a cooling rack. Brush the top with the remaining tablespoon melted butter. Let the panettone cool for at least 1 hour before cutting it.