Heat butter in a frying pan. Once foaming, brown the beef all over. Place on a grid over a roasting tin and cook at 220°C (200°C fan) mark 7 for 20min; cool.
Step 2
Place porcini in a bowl, add 30ml (2tbsp) boiling water; soak for 15min. Finely chop the shallots and flat mushrooms. Melt the butter. Add the shallots; cook for 1-2min. Add crushed garlic; cook for 30sec. Stir in mushrooms, porcini and soaking liquor. Cook for 5min until dry. Add thyme; season and cool.
Step 3
Roll out a quarter of the pastry to a rectangle 2.5cm (1in) larger than beef. Prick with a fork; bake at 220°C (200°C fan) mark 7 for 10-12min until very crisp and golden; cool. Season beef, spread mushroom mixture all over it, then wrap in the pancakes.
Step 4
Trim baked pastry to the size of the beef. Whisk egg; add a pinch of salt, then brush over pancakes. Place pastry on a baking sheet with the pancake-wrapped beef on top. Roll out remaining pastry to form a rectangle 30.5x40.5cm (12x16in). Cut a small square out of each corner; wrap around beef, tucking it under cooked pastry. Make a steam hole. Brush pastry with remaining egg; refrigerate. Cut trimmings into strips; arrange in a lattice pattern. Brush with egg.
Step 5
Cook at 220°C (200°C fan) mark 7 for 35min for medium rare, 40-45min, medium (see tip). Stand for 10min before serving. Garnish with thyme.
Step 6
Up to two days ahead, prepare mushroom mixture (step 2). Up to one day ahead, prepare the beef (steps 1 and 3), wrap and refrigerate. Bake the pastry as in step 3; cool and store. Wrap remaining raw pastry; refrigerate. Up to 4hr in advance, wrap the beef in the pastry as in step 4, wrap and refrigerate. Cover remaining egg; refrigerate. To serve. Remove beef from fridge 10min before baking. Brush with beaten egg; cook as in step 5.
An experienced and highly skilled team of food writers, stylists and digital content producers, the Good Housekeeping Cookery Team is a close-knit squad of food obsessives. Cookery Editor Emma Franklin is our resident chilli obsessive and barbecue expert, who spends an inordinate amount of time on holidays poking round the local supermarkets seeking out new and exciting foods. Senior Cookery Writer Alice Shields is a former pastry chef and baking fanatic who loves making bread and would have peanut butter with everything if she could. Her favourite carb is pasta, and our vibrant green spaghetti is her weeknight go-to. Lover of all things savoury, Senior Cookery Writer Grace Evans can be found eating crispy corn and nocellara olives at every opportunity, and will take the cheeseboard over dessert any time (though she cannot resist a slice of tres leches cake). With a wealth of professional kitchen know-how, culinary training and years of experience between them, they are all dedicated to ensuring every Good Housekeeping recipe is the best it can be, so you can trust they’ll work (and if they don’t – we’ll have the answer for why*) every time (*90% of the time the answer is: “buy an separate oven thermometer”!).
