Preheat the oven to 350°F and line an 8x8-inch baking dish with parchment paper.
Add the pecans, melted butter, and maple syrup to a food processor and pulse until the mixture is finely chopped and starts to hold together.
Press the crust mixture firmly into the bottom of the prepared baking dish.
Bake the crust for 10 minutes, then let it cool slightly.
In a large bowl, whisk together the mashed sweet potatoes, eggs, maple syrup, milk, melted butter, vanilla extract, cinnamon, salt, and nutmeg until smooth.
Pour the filling over the crust and spread it into an even layer.
Bake for 35 to 45 minutes, or until the center is set.
Let the bars cool completely, then chill before slicing for the cleanest cuts.