- With the rack in the middle position, preheat the oven to 350°F (180°C). Butter an 8-inch (20 cm) square pan and line with a strip of parchment paper, letting it hang over two sides.
- In a food processor, blend the hazelnuts, flour, maple sugar, baking powder and salt to a fine powder. Add the butter and pulse a few seconds at a time until finely chopped. Add the egg yolk and mix until smooth. Press the crust firmly into the bottom of the prepared pan.
- Bake for 18 minutes or until cooked and lightly golden.
- Meanwhile, in a bowl, whisk together the flour and cornstarch. Add the maple syrup and whisk to combine. Add the cream and egg. Whisk until smooth.
- Pour the filling over the crust while it is still hot. Bake for 35 minutes or until the filling is firm and lightly golden. Garnish with hazelnut halves, if desired. Let cool completely. Cut into squares. Freeze at this point, if desired.