Lamb Loin en Croûte with Mint & Pistachio Pesto

⏱ 150 min · Serves 4

A slimmer, faster cousin of beef Wellington: blushing pink lamb loin wrapped in a vivid mint-pistachio pesto, a savoury mushroom duxelles and burnished golden puff pastry. Slice it at the table and let the emerald spiral do the talking.

Per serving: 942 kcal · 58.0g protein · 41.0g carbs · 61.0g fat

Ingredients

• 2 x 400g lamb loin fillets (cannon of lamb), trimmed
• 1 tbsp olive oil
• 20g butter
• 2 sprigs thyme
• 320g all-butter puff pastry (1 sheet, or a 500g block rolled thin)
• 250g chestnut mushrooms, finely chopped
• 2 shallots, finely diced
• 1 garlic clove, crushed
• 2 tbsp dry white wine
• 6 slices prosciutto or Parma ham
• 1 egg, beaten with a pinch of salt
• Flaky sea salt and black pepper
• 40g fresh mint leaves
• 20g flat-leaf parsley
• 50g shelled pistachios, toasted
• 30g Pecorino, finely grated
• 1 small garlic clove
• 80ml extra virgin olive oil
• 1 tsp lemon juice
• Flour, for dusting

Method

1. Make the pesto: blitz mint, parsley, pistachios, Pecorino, garlic and lemon juice, trickling in the olive oil until you have a thick, spoonable paste. Season and set aside; you'll use half in the parcel and half for serving.
2. Duxelles: fry the shallots in the butter over medium heat for 4 minutes, add mushrooms, garlic and thyme leaves and cook 12–15 minutes until all the liquid has gone and the mix is dark and dry. Splash in the wine, cook it off, season, then cool completely.
3. Season the lamb loins hard. Heat the olive oil in a heavy pan until smoking and sear each loin for 60–90 seconds per side until deeply browned all over. Rest on a rack and cool to room temperature, then chill 20 minutes.
4. Lay a large sheet of cling film on the worktop. Overlap the prosciutto slices into a rectangle, spread with the cooled duxelles, then a thin layer of half the pesto.
5. Sit the two lamb loins end to end (or side by side, thick end to thin end, for an even log) on the ham. Use the cling film to roll into a tight cylinder, twist the ends like a cracker and chill 30 minutes to firm up.
6. Roll the pastry on a floured surface to about 3mm. Unwrap the lamb, sit it on the pastry, brush the borders with egg wash and roll up, sealing the seam underneath. Trim and tuck the ends. Chill 20 minutes more.
7. Heat the oven to 200°C fan / 220°C conventional with a baking tray inside. Egg wash the parcel all over, score lightly in a diagonal pattern and sprinkle with flaky salt.
8. Slide onto the hot tray and bake 22–25 minutes, until the pastry is deep golden and a probe in the centre reads 52–54°C for blushing pink.
9. Rest for 10 minutes (essential), then slice thickly with a serrated knife. Serve with the remaining mint pesto, and buttered new potatoes or spring greens.