Peel the sweet potatoes and cut them into 2 cm cubes. Spread the cubes over a baking tray lined with baking paper and roast for approx. 15 until tender. Use a hand blender to blend into a smooth purée. Stir in the paprika powder and oregano. Season with salt and pepper.
Press the garlic. Slice the shiitake mushrooms, chestnut mushrooms and onion. Heat 2 tablespoons of olive oil in a large frying pan, then fry the garlic, shiitake, mushrooms and thyme over a high heat for about 8 minutes until tender. Season with salt and pepper. Stir the shiitake and mushrooms into the sweet potato purée.
Heat the rest of the olive oil in the frying pan. Stir-fry the onion for 3 minutes over a medium-high heat until soft and translucent. Add the spinach in handfuls and stir until the spinach has completely wilted. Put the spinach in a sieve and press as much liquid out as possible with a wooden spoon. Mix the spinach into the sweet potato purée.
Crumble the feta and carefully mix into the purée. Taste, and season with salt and pepper if required.
Line a baking tray with the supplied baking paper. Place the puff pastry onto it. Spoon the purée filling lengthwise down the middle of the puff pastry. Leave a 2-3 cm border at both ends. Fold both sides of the puff pastry over the filling. Allow about 1 cm overlap and press firmly together using a little water. Carefully turn the roll over so that the seam is on the underside. If you have any pastry left over, cut out stars with a biscuit cutter from the remaining pieces. Attach them to the Wellington with a little water.
Beat the egg and brush over the pastry. Bake the Wellington in the middle of the oven for about 30 minutes until golden brown.
