- To make the pastry dough, place flour and baking powder in a food processor. Pulse several times to mix.
- Add cold butter. Lightly pulse (the butter should be pea-sized).
- In a bowl, mix egg, water, and vinegar. Set aside.
- Add this mixture to the flour mixture and pulse until it forms a ball. Remove dough from bowl.
- Cover with plastic wrap and refrigerate for 30 minutes.
- Portion into three balls and roll out as needed.
- Preheat oven to 180 °C (350 °F).
- In a saucepan, melt butter and add flour. Cook for 1 to 2 minutes.
- Wet mixture with 35% cream. Add maple syrup and vanilla. Slowly bring to a boil.
- Once it starts to bubble, stir well until thick. Remove from heat and let cool, stirring every 5 minutes to prevent a skin forming on top.
- On a floured surface, roll out dough into a 25-cm (10-in.) circle. Place pastry sheet into a 20-cm (8-in.) pie pan.
- Pour warm maple syrup mixture over the dough.
- Bake in the oven for 40–45 minutes.
- Remove and let cool.
Chef’s secret: This dough freezes very well. Make a large quantity so you always have some handy.