Remove frozen crust from the freezer when you start but don’t let it fully thaw before baking.
In a saucepan over medium-high heat, combine the maple syrup and balsamic vinegar. Bring to a boil, stirring frequently. Reduce the mixture until it thickens to about 1.5 cups. This process may take around 20 minutes, but times will vary—be patient!
Let the mixture cool to room temperature.
Prepare the Filling:
Coarsely chop the pecans using a food processor or knife and set aside.
In a mixing bowl, combine the eggs, brown sugar, reduced maple syrup mixture, salt, melted butter, and vanilla. Mix well. (Don’t worry if the butter and egg don’t fully combine; white ribbons are normal.)
Stir in the chopped pecans.
Assemble the Pie:
Pour the filling into the partially defrosted pie shell, spreading it evenly.
If there’s too much liquid, use a slotted spoon to transfer the pecans first, then add liquid if needed for a firmer filling.
Bake:
Place the pie on a cookie sheet and bake on the lower oven rack at 350°F for about 35 minutes, until the center puffs up and feels slightly firm.
For a golden crust, move the pie to the upper rack for the last 5–10 minutes of baking.
Cool and Serve:
Let the pie cool for at least 45 minutes before serving.
If making ahead, wrap the pie in cellophane and store at room temperature.
Serve with a scoop of vanilla ice cream for a perfect finishing touch!