- Move rack to middle of oven and heat to 400 degrees. Transfer cooled mushrooms to large bowl and combine with whole egg-egg yolk mixture.
- Place puff pastry on parchment-lined baking pan. Roll to remove any creases and to elongate slightly. Brush entire surface with egg wash and sprinkle on remaining 1/4 herbs. Spread mushrooms evenly over first 3/4 of pastry, leaving a 1-inch border around edges.
- Flip edge nearest to you over and lay it on the top 1/4 so puff pastry touches puff pastry, encasing mushrooms completely in a cylinder. Don't roll in pinwheel fashion as for strudel because the puff pastry in the interior will never bake and will become gummy.


