In a food processor, combine the flour, baking powder and salt. Add the butter and pulse a few seconds at a time until pea-sized pieces form. Add the water and pulse again until the dough just begins to form. Add more water, if needed. Remove the dough from the food processor and shape into a disc.
On a lightly floured surface, roll out the dough to a thickness of about 1/8 inch (3 mm). Line a 9-inch (23 cm) glass pie plate and remove excess dough. Refrigerate for 30 minutes.
With the rack in the lowest position, preheat the oven to 400°F (200°C).
In a bowl, combine the cornstarch and flour. Add the maple syrup and whisk until the mixture is smooth and the cornstarch has dissolved completely. Add the cream and egg. Whisk until smooth. Pour into the prepared crust.
Bake for 45 minutes or until the filling has set. Let cool at room temperature for 2 hours before serving.