In a saucepan off the heat, combine the syrup, cream, and cornstarch with a whisk. Add the butter. Bring to a boil and simmer gently for about 30 seconds, stirring constantly. Transfer to a bowl. Place plastic wrap directly on the filling. Let cool and refrigerate until completely chilled.
With the rack in the lowest position, preheat the oven to 200 °C (400 °F). Line a baking sheet with parchment paper.
On a lightly floured work surface, roll out the dough into a 25-cm (10-inch) square. Cut the dough into two rectangles of equal size. Place on the baking sheet. Cover and refrigerate for 30 minutes.
In a small bowl, combine the egg yolk and water. Set the egg wash aside.
On a floured work surface, cut a rectangle of dough into 12 long strips using a pizza cutter or a knife. Set aside.
Brush around the perimeter of the remaining rectangle of dough with water. Place strips of dough around the edge of the rectangle by using three strips, to prevent the filling from spilling. Spread the filling evenly in the centre of the rectangle up to the dough strips. Brush water around the edge of the dough. Place five strips of dough diagonally, spacing them evenly over the rectangle. Lightly press the strips around the edge. Brush water around the edge. Repeat with the remaining strips in the opposite direction, using the leftovers. Cut the edge of the pastry to remove any excess strips and even up the pastry. Brush the dough with the egg wash and sprinkle with maple sugar, if desired.
Bake for about 35 minutes or until the pastry is golden brown. Serve warm or at room temperature.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.