Lamb and Mushroom Shepherds Pie with Crisp Potato Top

Shepherds pie earned its name honestly: it is lamb under mashed potato. Most versions you meet are made with beef, which makes them cottage pie, and most of them taste flat because the filling is browned meat and gravy and nothing else. We fix that with mushrooms, and not as a garnish. Dried porcini go in for their soaking liquid. Fresh mushrooms go in browned hard in a dry pan. Between them the filling picks up a savory weight that ground lamb alone never quite reaches.

One tip before you start: brown the mushrooms in a dry pan before any fat goes in. They hold a lot of water. Add oil first and they steam in it, turn grey, and go rubbery. Dry pan, high heat, leave them alone. They squeak, they release, then they brown.

Ground lamb from a pasture raised animal is worth a call to a local farm. Shoulder ground is what you want, somewhere around 80/20. Leaner than that and the filling dries out under 30 minutes in a hot oven.

Why this lamb and mushroom shepherds pie works

• Two forms of mushroom. Dried porcini carry concentrated savory depth through their soaking liquid. Fresh mushrooms bring texture and browning. Neither does both jobs on its own.
• Dry heat first, fat second. Driving the water out before the oil goes in is the difference between browned mushrooms and stewed ones.
• Tomato paste and flour get cooked in. Two minutes in the hot pan takes the raw edge off both and gives the filling body without a pasty taste.
• An egg yolk in the mash. It sets in the oven, so the ridges brown and hold their shape instead of slumping.
• The filling goes in cool. Hot filling melts the butter out of the mash before the dish ever reaches the oven.

Ingredients

For the filling

• 2 lb ground lamb (900 g), around 80/20, shoulder ground if you can get it
• 1 lb fresh mushrooms (450 g), cremini and shiitake, quartered
• 1 oz dried porcini (28 g)
• 1 1/2 cups hot water (360 ml) for soaking
• 2 tbsp olive oil or rendered tallow
• 1 large onion, diced
• 2 carrots, diced small
• 3 garlic cloves, minced
• 2 tbsp tomato paste
• 2 tbsp all purpose flour
• 1 cup dry red wine (240 ml)
• 1 tbsp Worcestershire sauce
• 2 tsp fresh thyme leaves
• 1 tsp kosher salt, plus black pepper to taste
• 1 cup frozen peas (140 g)

Substitutions: dried shiitake stand in for porcini and give a smokier result. For an alcohol free version, use stock plus 1 tbsp red wine vinegar. Cornstarch slurry replaces the flour if you need it gluten free.

For the potato top

• 3 lb Yukon Gold or russet potatoes (1.35 kg), peeled and cut into 2 inch chunks
• 6 tbsp butter (85 g)
• 1/2 cup whole milk or cream (120 ml), warmed
• 1 egg yolk
• 1/2 cup grated Parmesan or aged cheddar (50 g)
• 1 tsp kosher salt

Method

1. Soak the porcini. Cover the dried porcini with the hot water and leave 20 minutes. Lift them out and chop them. Pour the liquid off the grit that settles at the bottom, or strain it through a cloth. That liquid carries most of the flavor in this dish, so none of it goes down the drain.
2. Boil the potatoes. Salt the water heavily and cook the potato chunks 15 to 18 minutes, until a knife slides in with no resistance. Drain them, then let them steam dry in the hot pot for 2 minutes. Wet potatoes make loose mash.
3. Mash and cool. Push the potatoes through a ricer or work them with a wooden masher, then beat in the butter, warm milk, cheese and salt. Let the mash cool about 10 minutes before you stir in the egg yolk. Added to mash straight off the stove, the yolk scrambles.
4. Brown the mushrooms dry. Heat a dry cast iron skillet over high heat. Add the fresh mushrooms in one layer and leave them alone 3 to 4 minutes. They squeak, then release their water, then start to brown. Once the pan is dry again, add 1 tbsp of the oil, toss for 2 minutes, and tip them into a bowl.
5. Brown the lamb. Same pan, medium high heat, remaining oil, lamb pressed into a flat layer. Leave it 4 minutes to build a crust before you break it up, then cook 4 minutes more. Pour off all but about 2 tbsp of the fat.
6. Build the base. Add the onion and carrot and cook 6 minutes until softening. Garlic for 1 minute. Then tomato paste and flour together, stirring hard for 2 minutes until the paste darkens to brick red.
7. Deglaze. Pour in the wine, scrape the bottom of the pan, and simmer about 3 minutes until it has nearly cooked away.
8. Simmer the filling. Add the porcini liquid, chopped porcini, browned mushrooms, Worcestershire, thyme, salt and pepper. Simmer uncovered 20 minutes, until a spoon dragged across the pan leaves a trail that holds for a second. Stir in the peas, take it off the heat, and let it cool 15 minutes.
9. Assemble. Heat the oven to 400F (205C). Spread the filling in a 9 by 13 inch dish or straight into the skillet. Spoon the mash over in dollops, then join them with the back of a spoon so the filling is sealed right to the edges. Drag a fork across the top. Those ridges are what brown.
10. Bake. 30 to 35 minutes, until the filling bubbles at the edges and the top is set. Then broil 3 to 5 minutes for color, watching it the whole time.
11. Rest. Give it 10 minutes before serving. Straight from the oven the filling is molten and will not hold a cut edge.

Pro tips and common mistakes

• Cool the filling first. Warm filling turns the underside of the mash to soup and it never sets properly.
• Seal the mash to the rim. Gaps let the filling boil up and over, and the whole top slides sideways.
• A thin filling at 20 minutes stays thin. It will not thicken in the oven, so keep simmering until the spoon leaves a trail.
• Skip the piping bag. A fork dragged across the surface gives better ridges than piped rosettes, and there is no plastic to wash afterward.
• Lean lamb needs help. If 85/15 is all you can find, stir 2 tbsp butter into the filling at the end.

Storage and leftovers

Covered in the fridge it keeps 4 days, and it cuts far better cold than hot, so leftovers come out in neat squares. Reheat at 350F for 20 to 25 minutes, uncovered so the top crisps again.

The whole pie freezes well unbaked. Assemble it, cool it completely, wrap it and freeze up to 3 months, then bake from frozen at 375F for about 1 hour 15 minutes. Baked leftovers freeze too, though the mash turns grainier on the second thaw.

What to serve with it

• Buttered peas with mint, if you left the peas out of the filling.
• Pickled red cabbage, sharp and cold against a rich filling.
• A green salad with a mustard vinaigrette.
• Malt vinegar on the table. Some people want it, and they are not wrong.

Nutrition

About 710 calories, 35g protein, 38g fat, and 57g carbs per serving. These are estimates and vary with the exact cut, trim, and any substitutions.

Frequently asked questions

Is this shepherds pie or cottage pie?

Shepherds pie is lamb. Cottage pie is beef. Menus swap the two names constantly, but the lamb version came first and it is what this recipe makes.

Can I use fresh mushrooms only?

You can, and it will still be good, but you give up the porcini liquid where most of the savory depth lives. If you skip the dried mushrooms, replace that liquid with strong beef or lamb stock and add 1 tsp soy sauce.

Why did my potato topping sink?

Almost always because the filling went in hot, too loose, or both. Cool it, and simmer it until it holds a trail behind the spoon.

Can I make it ahead?

Yes, and it improves for it. Assemble up to 2 days ahead and refrigerate unbaked, then add 10 to 15 minutes to the bake time because it starts cold.

What potatoes work best?

Russets give the fluffiest top. Yukon Golds are creamier and hold together better under a fork. We use Yukon Golds and a ricer.

Where to buy the lamb

Ground lamb varies more than any other ground meat, because what goes into it depends entirely on the butcher. Shoulder gives you the fat and the flavor this dish needs. Ask a producer near you through our Find a Farmer directory for ground lamb shoulder at around 80/20, and ask whether they can grind it fresh for you.

More on the cut behind the grind in our lamb shoulder guide, and on the animal as a whole in the lamb wiki. The filling here is a braise, so our guide to braising covers the technique. For more lamb, try the braised lamb shanks or a roast leg of lamb.