Preheat the oven to 200°C fan (220°C conventional, gas 7).
Heat a drizzle of olive oil in a large pan. Add the chopped mushrooms, chestnuts and tamari and cook for a few minutes until the mushrooms soften and brown.
Add the well drained lentils, crushed garlic, gravy granules, tomato puree, dijon mustard and the chopped rosemary and thyme, and mix.
Cook for 2 minutes, then take off the heat and cool for 5 to 10 minutes.
Place the first pastry sheet onto a baking tray and spoon the filling down the middle, leaving a border. Pile it about 5cm high and keep it compact.
Lay the second pastry sheet on top and press firmly around the filling and edges.
Trim any excess pastry (save it for shapes), crimp the edges with a fork, score a few lines on top to let steam out and lightly brush with olive oil.
Bake for 20 minutes until golden. Rest for 5 minutes, then slice with a serrated knife.
Video
Notes
Make Ahead:Assemble the Wellington the day before, cover and keep it in the fridge. Glaze and bake on the day, adding about 5 minutes. Or bake it fully, cool, chill for up to 2 days and reheat once at 180°C fan (200°C conventional, gas 6) for 15 to 20 minutes until piping hot. Do not store it at room temperature.To Freeze:Wrap the unbaked Wellington well and freeze for up to 3 months. Defrost in the fridge overnight, then glaze and bake as normal until piping hot.Ingredient Swaps:
Chestnuts: Walnuts or pecans
Tamari: Soy sauce (if you do not need it gluten free)
Gravy granules: Vegetable stock powder
Fresh herbs: 1 tsp each of dried rosemary and thyme
Top Tips:
Be gentle when placing the pastry over the filling and when crimping the edges with a fork.
Brush with olive oil before scoring if you want the score marks to stand out more.
Allow to cool for 5 minutes before slicing so the filling holds together.
Slice with a serrated knife to cut cleanly through the pastry.