Put all the ingredients for the pastry in a food processor and pulse until homogeneous; if necessary, add 1 or 2 tablespoon of water.
With the dough, prepare 2 balls (2/3 and 1/3 respectively of the dough) and keep in the refrigerator for at least 30 minutes.
Put the sugar, water and honey in a large heavy-based saucepan over medium heat. Stir gently to dissolve the sugar. Bring to the boil and let it continue to boil until it becomes a dark golden color. Stir from time to time.
Add the nuts and the cream and stir the walnuts until well coated.
Remove the saucepan from the heat and. Set aside to cool.
Preheat the oven to 180°C Grease a 30 cm tin (heat and timing are basing it on convection oven).
Roll out the larger ball between two sheets of cling film to a 34 cm circle and use it to line the tin of 30 cm square. Press the edges of the pastry against the side of the tin.
Scrape the filling onto the pastry. Level the top as well as you can, but don’t apply too much pressure, or you may tear the pastry and the filling will leak out. Fold the excess pastry inwards over the filling.
Roll the second piece of pastry to a neat 29 cm circle. Moisten the edges of the pastry base in the tin with the egg white and position the second pastry circle on top of this. Use a fork to crimp and seal the edges Mix the reserved egg yolk with 2 tablespoon cream and brush the cover. Prick with a fork in several places. If you like, you can score a plaid pattern onto the surface with the fork.
Bake for 35-40 minutes, or until golden brown. Leave to cool until lukewarm in the tin, then loosen the sides, release the clip and carefully transfer the pie to a wire rack to cool completely.