First make the crust. Cut the cold butter into cubes and mix them with the flour to get buttery crumbs.
Make a well in the flour and add the ground walnuts, 2 eggs and the sugar. Knead the crust quickly so that the butter doesn't melt - otherwise the pie will end up soggy. Wrap the crust in foil and leave it for 30 min. in the fridge.
Crumble the biscuits into small pieces and pour them into a bowl. To them add the ground walnuts and sugar. Dice the peeled and cleaned of seeds pears to about 1/2″ (1 cm) per side. Add them to the bowl also.
Mix well. Set aside about 1/3 of the crust. Lay out the rest of it along the bottom and sides of a pie form about 10″ (26 cm) in diameter.
You can lay it out with your hands or use a rolling pin to flatten it out ahead of time. Pour the filling on top and even it out. Cut out strips from the rest of the crust and make a crisscross weave on top of the pie.
Smear with egg yolk on top (use a brush) and sprinkle with a little brown sugar. Bake the pie in a preheated oven for 40 min. or until it gets a nice golden color. Leave it to cool and serve.