Preheat the oven to 350ºF (180°C). Line a baking sheet with parchment paper.
On a clean surface, have 1 cup clarified butter ready and a pastry brush. Cut 8 phyllo sheets into 4 pieces (I use scissors).
Arrange one sheet on a flat surface and brush, carefully, with clarified butter. This is easier if you dot the entire dough with small amounts of butter and then spread. If you tear it, don't worry, patch it up as best as you can. Repeat with the remaining three sheets of phyllo dough, stacking them one on top of the other.
Sprinkle 2 tablespoons dry breadcrumbs along one short side, leaving 3 or 4 inches from the border.
Put the cooled mushroom mixture on top of the breadcrumbs, then sprinkle 3 tablespoons pecans or walnuts on top.
Starting on the short side near you, fold the dough over the filling. Brush the dough with butter.
Fold the two sides inwards. Fold the packet as many times as necessary, brushing the dough with butter every time. When you're done folding and you have a tight packet brush the entire surface with butter making sure the dough is sealed.
Bake for 30 minutes, until golden brown and crisp.
Cool to room temperature, cut into slices and serve.