Preheat oven to 350 degrees F (180 degrees C).
In a small bowl, mix the cornstarch with 4 teaspoons water, adding 1 teaspoon of water at a time and mixing after each addition. Stir until combined into a milky liquid with no lumps.
Melt the butter in a bowl in the microwave. Whisk in the brown sugar.
Add the maple syrup, vanilla, flax eggs, and salt and whisk again to combine. Add the cornstarch mixture, and whisk again.
Place pie crust on a baking sheet. Fill the pie crust with chopped pecans, spreading them out evenly.
Pour the filling mixture over the top of the pecans, and arrange the extra whole pecans on top as desired.
Make for 30 to 35 minutes, until the pie is mostly set but the center still jiggles slightly.
Leave on baking sheet for about 10 minutes before carefully transferring to a plate to cool.