Start by cutting your whole grain bread into cubes or large chunks. If your bread is fresh, consider toasting it lightly or letting it sit out for a bit to dry. This helps the bread soak up the custard without turning mushy.
In a large bowl, whisk together the eggs, milk, brown sugar, molasses, ground ginger, cinnamon, nutmeg, vanilla extract, baking powder, and salt. Whisk until the mixture is smooth and well combined, and the brown sugar has mostly dissolved.
Place the bread cubes in the prepared baking dish. Pour the gingerbread custard evenly over the bread, gently pressing down with a spatula or your hands to ensure every piece is soaked. Sprinkle the chopped pecans or walnuts evenly on top.
Cover the dish with plastic wrap or a lid and refrigerate for at least 2 hours, or ideally overnight. This soaking step allows the bread to absorb all the warm, spicy goodness of the custard.
Preheat your oven to 350°F (175°C). Remove the casserole from the fridge and bake uncovered for 45-50 minutes, or until the custard is set and the top is golden brown and slightly crisp.
Let the casserole cool for about 10 minutes before serving. Dust the top with powdered sugar and drizzle with maple syrup. Serve warm and enjoy the cozy flavors!
