Preheat the oven to 350°F (180°C) and line an 8-inch (20cm) square baking pan with aluminum foil. Set aside.

In the bowl of a food processor or in a large mixing bowl, whisk together the flour, powdered sugar, cornstarch, and salt.

Add the cold butter and pulse or cut in with a pastry blender until the mixture resembles damp crumbs and starts to clump together

Gather the dough into a ball and then transfer to the prepared baking pan and press the dough evenly into the bottom.

Prick all over with a fork and bake until the crust is dry and pale golden, about 15 minutes.

Remove the crust from the oven and turn the heat up to 400°F (200°C).

Spread the pecans evenly over the warm crust.

In a small mixing bowl, lightly beat the eggs and set them aside.

Cook the maple syrup and sugar in a small saucepan fitted with a candy thermometer over medium heat until the temperature registers 225°F (110°C).

Very gradually drizzle the hot syrup into the eggs, whisking constantly to prevent curdling.

Strain the mixture into a glass measuring cup with a pour spout and then whisk in the butter, vanilla extract, and salt.

Pour the maple syrup mixture evenly over the pecans in the crust and bake for 10 minutes.

After 10 minutes, lower the heat to 350°F (180°C) and bake for another 20-30 minutes, until the edges are set and the filling is bubbling.

Let cool completely in the pan before removing and cutting into 9 squares. Store, loosely covered, at room temperature for up to 3 days.