Butter the inside of an 8x8 baking dish, and set aside.
Pour the maple syrup into a medium sauce pan over medium heat.
Bring the maple syrup to a simmer, and then pour in the milk. Stir the mixture together until smooth.
Let the mixture simmer and thicken for about 2 minutes, stirring constantly. You can reduce the heat to medium-low if needed to keep it from boiling. After 2 minutes, turn off the heat.
Crack the eggs into a medium bowl, and gently stream about 1/2 c of the maple-milk mixture into the eggs while whisking the eggs constantly. This is how you temper the eggs to bring them to a higher temperature before adding them in with the rest of the custard. This step is necessary to avoid scrambled eggs! Once the eggs are completely whisked with no white streaks, pour the egg mixture into the pan, whisking constantly, to incorporate it into the custard.
Add the vanilla and cinnamon, and mix until completely smooth and combined.
Place the cubed gluten free bread into a large bowl, and pour the custard on top. Mix it together thoroughly so all of the bread pieces are covered in the custard.
Cover the bowl and let sit at room temperature for 30 minutes so that the custard can get absorbed.
Meanwhile, preheat oven to 350.
Transfer the bread to the buttered baking dish, and smooth it into an even layer.
Bake for about 45 minutes, until the bread pudding is puffed, lightly golden brown, with a slightly jiggly center. A toothpick inserted in the center should come out clean.
Place the bread pudding on a wire rack to cool. Serve warm or at room temperature!