1. Soak the porcini in boiling water for 15 minutes, then drain and chop. Melt 25g of the butter in a large frying pan and gently fry the shallots and garlic for 5 minutes until soft. Add all the mushrooms and cook over a high heat for 3-4 minutes until golden and just tender. Remove from the heat and stir in the Madeira, parsley, chestnuts, pine nuts and seasoning. Leave to cool.
2. Preheat the oven to 200°C, gas mark 6 and line 2 large baking sheets with parchment. Steam the spinach for 2 minutes until wilted, then squeeze out any water. Melt the remaining butter. Divide the mushrooms and spinach into 12 equal portions.
3. Lay a clean tea towel on the work surface. Place the stack of pastry sheets with the short end nearest to you. Using scissors, cut the sheets in half lengthways. Take one length of pastry. Brush with butter. Spread 1 tsp of the tomato paste in a circle on the end nearest to you, leaving a 2cm border around it. Top with one portion each of the spinach and mushrooms.
4. Fold the bottom left corner of pastry over the filling to make a triangle. Then fold the triangle up once, along its top edge. Continue folding in this way, from right to left and visa versa, to make a triangular shape and enclose the filling. Use a little melted butter to stick the seam.
5. Lift the parcel onto the baking sheet, seam-side down, and brush with more melted butter. Repeat to make a total of 12 parcels. Bake for 18-20 minutes or until golden. Remove from the oven and immediately dust with sumac and cinnamon. Meanwhile, mix the tahini, lemon juice, yogurt and seasoning together. Serve with the samosas.