A bloke came through the pass at a place I worked near Maitland years back and sent his gratin straight to the bin because it had “gone to soup” on the plate. Fair call, honestly. A watery gratin is one of those dishes that looks the part going into the oven and lets you down the second you cut into it. I’ve made that mistake plenty of times myself, usually by rushing the sauce or not salting the potato properly beforehand.
This leek and potato gratin with a lighter sauce is the version I’ve landed on after a lot of Sunday afternoons with the oven on and the kitchen smelling like onions. It still has that golden, blistered top and the slow give of properly cooked potato underneath, but the sauce is built from milk and a bit of reduced stock instead of a full cream and butter bomb. It holds. That’s the whole point.
Why the lighter sauce actually works
Most gratin sauces are a straight bechamel, which is flour, butter and full cream milk cooked out until it coats a spoon. There’s nothing wrong with that, but it’s heavy, and if you’re after something you can eat for lunch a few times a week without feeling like you need a lie down afterward, it’s worth rethinking.
What I do instead is sweat the leeks properly first, low and slow, so they give up their own sweetness and a fair bit of liquid. Then I build the sauce around reduced vegetable or chicken stock with a splash of milk, thickened with a small amount of cornflour slurry rather than a full butter-and-flour roux. You still get body. You still get that cling to the back of a spoon. You just don’t get the same load of saturated fat sitting on top of all that potato.
Nutrition Australia and most of the dietary guidelines out of eatforhealth.gov.au aren’t saying cream is the enemy, they’re saying balance across the week matters more than any one dish. A gratin like this lets you have the comfort food without it being the only vegetable-heavy thing you eat all week.
Getting the leeks right before anything else
Don’t muck about with dirty leeks. Slice them into half-moons, dunk the lot in a big bowl of cold water, swish it around and let the grit sink. Lift them out rather than tipping the water off, because otherwise you’re just pouring the dirt straight back over your leeks. I learned that one the hard way in a commercial kitchen with a head chef who did not find it funny.
Get your pan properly hot, a decent glug of olive oil, and cook the leeks down slowly with a lid half on. You want them collapsed and sweet, not coloured. If they start catching, your heat’s too high and you’ll end up with bitterness running through the whole dish.
The potato matters more than people think
A waxy potato like a Nicola or a Kipfler holds its shape through baking, which is what you want for layers you can actually serve rather than scoop. A floury spud like a Sebago will break down and go gluey, which some people like but I don’t rate for this particular dish. Slice them about four millimetres thick on a mandoline if you’ve got one, because even slices cook evenly and that’s half the battle with a gratin.
Ingredients
- 1kg waxy potatoes (Nicola or Kipfler), peeled
- 3 medium leeks, white and pale green parts only, washed and sliced into half-moons
- 2 tbsp olive oil
- 2 garlic cloves, finely chopped
- 300ml reduced-fat milk
- 250ml vegetable or chicken stock, good quality
- 1 tbsp cornflour mixed with 2 tbsp cold water
- 1 tsp Dijon mustard
- 60g grated tasty cheese, plus extra for the top
- 30g finely grated parmesan
- Sea salt and black pepper
- A grating of fresh nutmeg
- 2 tbsp fresh breadcrumbs, for the top
Method
- Preheat your oven to 190°C fan-forced. Grease a baking dish roughly 25cm x 20cm.
- Get a wide heavy-based pan properly hot over medium heat and add the olive oil. Add the leeks and a good pinch of salt, drop the heat to low, and cook with the lid half on for about 12 minutes, stirring occasionally, until they’re soft and sweet with no colour on them.
- Add the garlic and cook for another minute until fragrant.
- Pour in the stock and milk, bring to a gentle simmer, and let it tick along for a few minutes to come together.
- Stir in the cornflour slurry and keep stirring until the sauce thickens enough to coat the back of a spoon, about two to three minutes. Stir through the Dijon mustard, the nutmeg, and season well with salt and pepper. Taste it here, because this is where you fix it, not after it’s baked for forty minutes.
- Slice the potatoes about 4mm thick, ideally on a mandoline, and layer a third of them across the base of the dish, overlapping slightly.
- Spoon over a third of the leek sauce and scatter a third of the tasty cheese. Repeat the layers twice more, finishing with sauce and cheese on top.
- Scatter the parmesan and breadcrumbs over the top layer.
- Cover with foil and bake for 35 minutes. Remove the foil and bake a further 25 to 30 minutes until the top is golden and a knife slides through the potato without resistance.
- Rest for ten minutes before serving. This isn’t optional, it’s how the sauce sets back into the layers instead of running everywhere.
What to put next to it
This gratin is rich enough to carry a meal on its own with something sharp alongside it. I’d reach for the shaved fennel and orange salad done properly because the citrus cuts straight through the richness and wakes the whole plate up. A simple green salad with a mustardy dressing does the same job if fennel’s not in the crisper that week.
If you want it as a proper lunch rather than a side dish, a poached egg on top with the yolk running into the layers is no bad thing. I won’t pretend that’s authentic to anything, it’s just good.
A variation worth trying
Swap half the potato for thinly sliced celeriac if you want more vegetables in the mix and a slightly different texture, a bit more silky where the potato is more structured. I’ve also done this with a layer of sautéed silverbeet folded through the leek sauce when I had a glut of it from the garden, and nobody complained.
If you’re trying to get more vegetables into a household where tastes run in different directions, this dish is a decent Trojan horse. I’ve written before about cooking one dinner for five different appetites and a gratin like this sits in that same category, mild enough for fussy eaters, interesting enough that it doesn’t feel like a compromise for everyone else at the table.
The bit I’d argue with other recipes about
I’ll say the quiet part here: a lot of “healthy” gratin recipes skip the cheese entirely or go for some reduced-fat substitute that doesn’t melt properly, and the result is a dish that tastes like it’s apologising for existing. I’d rather use real tasty cheese and parmesan in a smaller amount than a bigger amount of something that won’t brown. Flavour matters more than shaving off the last few grams of fat, and Better Health Victoria’s guidance on this is pretty sensible too, it’s about the pattern of what you eat, not any single dish being perfect.
Getting ahead on a busy week
You can assemble this the night before and keep it covered in the fridge, then bake it straight from cold, adding about ten minutes to the covered baking time. It also reheats well in a moderate oven the next day, better than the microwave which turns the top rubbery. If you’re building out a pantry that makes dishes like this easier on a Tuesday night, have a look at setting up a healthy weeknight pantry that actually works, because half of cooking well through the week is just having the right things already in the cupboard.
Leftovers, if there are any, sit well on the side of a roast chicken the next night, or chopped up and fried in a pan with a fried egg on top for breakfast. That’s not in any cookbook I own, it’s just what happens in my kitchen on a Monday.
– Dave Forsythe, Golden Door Living kitchen
