Here are four steps to ensure puff pastry comes out perfect every time. The leading cause of soggy puff pastry is moisture. Step 1 Let the meat come to room temperature. Pat dry with a paper towel, lightly salt, and let rest for 5 minutes, pat dry with a paper towel. The meat is free of excess moisture and ready. Step 2 Chop the mushrooms and onion finely, and cook them at high heat, constantly stirring until the moisture from the onions and mushrooms evaporate. Step 3 Egg wash the inside of the puff pastry. Egg-wash cooks quickly and creates a barrier to protect the puff pastry. Step 4 Add 2-3 steam vents to the top to allow steam to escape. Preheat the baking tray before adding the wellington. Furthermore, do not overcook wellington.