- Preheat the oven to 350F and line the baking tray with parchment paper.
- For the filling, melt chocolate and butter separately in a microwave. Heat in 30 second intervals, mixing between each interval for both.
- Combine melted chocolate and butter with the crushed hazelnuts and salt. Set aside.
- Working with one fillo sheet at a time (the rest should be covered with a clean damp tea towel to prevent from drying out), brush melted butter on each fillo sheet placing one on top of the other. Repeat with all the of the sheets.
- To assemble, spread the filling mixture over 1/4 of the fillo sheets, leaving a 1 inch border across all sides.
- Starting from the side with the filling, gently roll the sheets and place the strudel onto the baking tray. Be sure to place the seam of the fillo strudel at the bottom.
- Brush strudel with egg wash and bake for 30 minutes or until golden brown. Remove from the oven and let cool before dusting with powdered sugar and chocolate drizzle. Garnish with additional toasted hazelnuts.