Allow the puff pastry to thaw on the counter top about 40 minutes or according to package directions. After half of the thawing time, begin preparing the recipe.

Preheat the oven to 400 degrees F.

Chop the mushrooms and onion until diced fine.

Combine the mushrooms, onion, garlic and thyme in a bowl.

Melt another tablespoon of butter in the same frying pan over medium heat.

Add the mushroom mixture and cook until lightly browned, about 5 minutes.

Sprinkle the mushroom mixture with salt and freshly ground pepper to taste and set aside to cool.

On a lightly floured surface, roll the puff pastry sheet into a 14 x 10 inch rectangle. Cut in half to make two 7 x 10 inch rectangles.

Divide the mushroom mixture and add half to the center of each rectangle.

Place one steak on top of the mushrooms on each rectangle.

Lightly brush pastry edges with water.

Bring the opposite corners of the pastry over the steak and pinch seams to seal tightly.

Cut three small slits in the top of each pastry bundle.

Brush all over the pastry bundles with beaten egg.

Bake for 25-30 minutes or until pastry is golden brown and meat reaches desired doneness. For medium-rare, a thermometer should read 145 degrees F, for medium 160 degrees F, for well-done 170 degrees F.