1. Pre-heat the oven to 220°C.
2. For the stuffing, soften the shallots in 30g of the butter, and then add the mushroom, thyme and garlic.
3. Soften all the mushrooms adding a little more butter if necessary and then add the breadcrumbs. Allow them to cool and season well.
4. For the venison and pastry, sear the venison all over in the butter and let it cool. Dust your work surface with some flour and roll out the pastry to fit the meat like a parcel; it should be thin but supple.
5. To assemble it, put half of the stuffing on top of the roll out pastry. Place the venison on top of that, followed by the rest of the stuffing.
6. Mix together the egg wash ingredients and brush the pastry edges. To avoid making a clumsy, pastry-heavy parcel, cut out and discard the four corners, then wrap it all up, folding the short ends over first and then the long sides.
7. Brush the pastry with the egg wash. Now take another long piece of pastry, roll out then hold the pastry at the front, then with a lattice cutter make one clean cut, gently spread it out with your hands to make the holes.
8. Place over the pastry and make sure it’s well tucked in.
9. Brush over with some more egg wash. Put it into the oven for 25 to 30 minutes, reducing the heat to 200°C after 10 minutes.
10. At this point, it is useful to have a probe for testing the meat. The temperature should not rise above 50°C. It will, and should be rare.