Shepherd's Pie

Steps

1. Boil20 min
   start in cold salted water, then a steady simmer
   • potato
   potato + water + 1 tsp of the salt, until a knife meets no resistance at the center — starting cold heats the piece evenly, where dropping cold potato into boiling water blows the outside to mush before the middle gives
2. Mash6 min
   off heat, potato still steaming
   • butter
   • milk
   drained potato returned to the dry hot pan for a minute to drive off surface water, then + butter + warm milk, mashed by hand — a food processor shears the cells open and the freed starch turns the mash to glue that will never take a fork ridge
3. Sear8 min
   high, wide pan, left undisturbed
   • lamb
   lamb pressed into a thin layer, browned hard on one side before breaking it up, then lifted out and all but about a tablespoon of the rendered fat poured off — leave it all in and the fat separates in the oven and pools greasy under the mash
4. Saute8 min
   medium, in the reserved lamb fat + olive oil
   • onion
   • carrot
   • celery
   • garlic
   onion + carrot + celery until soft and just golden, then + garlic for the last minute; the vegetables are cut fine so they surrender into the gravy rather than sitting in it as chunks
5. Caramelize3 min
   medium
   • tomato paste
   + tomato paste, stirred flat against the pan until it darkens from red to brick — raw paste stays sour and tinny, cooked paste is the backbone of the gravy's depth
6. Simmer28 min
   low, uncovered
   • flour
   • beef stock
   • thyme
   • rosemary
   • bay leaf
   • black pepper
   + flour stirred in for a minute to coat everything, then + beef stock + worcestershire + thyme + rosemary + bay leaf + browned lamb + pepper + remaining salt, reduced until a spoon dragged through leaves a track that closes slowly — a loose filling boils up through the mash and floods the top
7. Fold2 min
   off heat
   • green peas
   + peas, and discard the bay leaf and thyme stems; peas added at the start of the simmer go army-grey and mealy, added now they stay green and sweet
8. Rest15 min
   filling spread in the baking dish, uncovered
   let the filling cool until it stops steaming — mash spooned onto molten gravy sinks and disappears into it instead of sitting as a lid
9. Top4 min
   mash spread from the edges inward so it seals to the rim of the dish, then raked all over with a fork — those ridges are the whole point of the browning, since only the raised edges get hot enough to color
10. Bake25 min
    400°F / 200°C
    until the gravy is visibly bubbling at the sealed edges, which is the only reliable sign the center of the filling is actually hot
11. Broil4 min
    high, watched constantly
    until the fork ridges are deep brown and crisp; the browning is surface work and goes from golden to burnt in under a minute, so stay at the oven door