Gather all ingredients and ensure eggs are at room temperature, as this creates a smoother, more evenly textured custard. In a large bowl, whisk together the eggs, whole milk, maple syrup, vanilla extract, salt, ground cinnamon, and ground nutmeg until fully combined and no streaks remain. The room-temperature eggs incorporate more smoothly into the milk, creating a silkier custard that will absorb evenly into the bread. Set the custard mixture aside while you prepare the slow cooker.

Lightly grease the slow cooker with butter or cooking spray. Cut the stale brioche bread into 1-inch cubes—stale bread is crucial here as it will absorb the custard without turning mushy or falling apart. I prefer stale bread because it has already lost some moisture, so it soaks up the egg mixture more effectively than fresh bread. Spread the bread cubes evenly in the greased slow cooker, then scatter the chopped pecans throughout, distributing them in an even layer so every bite has some nuttiness.

Pour the custard mixture from Step 1 evenly over the bread and pecans in the slow cooker, then gently stir to ensure the bread is partially submerged and the custard is distributed throughout. In a small bowl, combine the packed brown sugar with 1 tsp ground cinnamon and mix until the cinnamon is evenly distributed—this prevents clumping and ensures consistent spice flavor in every bite. Sprinkle this brown sugar-cinnamon mixture evenly over the top of the casserole, then drizzle the melted and slightly cooled butter over the entire surface. The butter helps the topping brown slightly and adds richness.

Cover the slow cooker and cook on HIGH for 2 to 2.5 hours, or on LOW for 3 to 4 hours, depending on your schedule. The casserole is done when the custard is set but still has a slight jiggle in the center—it will continue to firm up as it cools slightly. I like to check it at the minimum time and then check every 15 minutes after that, as slow cookers vary in temperature. The bread should be golden brown on top and the edges should pull away slightly from the sides of the slow cooker. Let it rest in the slow cooker for 5-10 minutes before serving to allow the custard to fully set.