Step 1

Adjust oven rack to middle position and heat oven to 350 degrees. Grease 12-inch cast-iron skillet with softened butter. Mix brown sugar, cinnamon, nutmeg, and salt together in bowl.

Step 2

Sprinkle 2 tablespoons brown sugar mixture over bottom of prepared skillet. Arrange half of bread pieces in even layer in skillet. Drizzle with 1½ tablespoons melted butter and sprinkle with 2 tablespoons brown sugar mixture. Repeat layering with remaining bread pieces, 1½ tablespoons melted butter, and 2 tablespoons brown sugar mixture.

Step 3

Whisk milk and eggs together until well combined, then pour mixture over bread and press gently to help bread soak up egg mixture. Sprinkle with almonds and remaining brown sugar mixture.

Step 4

Transfer skillet to oven and bake until casserole is slightly puffed and golden brown and bubbling around edges, about 30 minutes, rotating skillet halfway through baking.

Step 5

Using potholders, transfer skillet to wire rack, brush casserole with remaining 1 tablespoon melted butter, and let cool for 15 minutes. Sprinkle with confectioners' sugar and serve.