Cut any kind of bread into 1-inch cubes - I recommend a crusty, whole grain variety, but sandwich bread will work, too. Just use enough slice to fill a lightly greased 9x13-inch baking dish quite full.
In a large bowl, whisk together eggs, milk, vanilla, pumpkin butter and pie spice until well combined. Pour over bread and push down with a spoon or your hands until it's all soaked and mostly covered. Cover with saran wrap or lid and refrigerate overnight.
In the morning, preheat oven to 350 degrees F (176 C), uncover and top with brown sugar, additional pumpkin pie spice and nuts (optional). Bake for 35-45 minutes or until golden brown and no longer wet.
Serve immediately with maple syrup, honey or agave nectar. Store leftovers in the refrigerator covered for up to a couple days.
*For the bread cubes, just use as much bread as it takes to fill the bottom of your dish generously, plus up about 1 to 1.5 inches. If you've added too much to soak up the liquid, just remove some. And if it looks too wet, add some more bread. *I used 2%, but use skim or low-fat for a lighter recipe. Alternatively, use non-dairy such as soy or almond. *I HIGHLY recommend using pumpkin butter, as it has a concentrated pumpkin flavor and is much sweeter than puree. But if using puree instead of butter, it's important to compensate the flavor by adding a bit more puree, pumpkin pie spice, and a little agave nectar, brown sugar or maple syrup to the batter. Otherwise, it will lack that delicious fall, pumpkin flavor you're going for.