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Traditional Finnish imelletty perunalaatikko in a white baking dish on a wooden table, photographed in soft Nordic daylight.
Erik Lundström

Imelletty Perunalaatikko – Finnish Sweetened Potato Casserole

Imelletty perunalaatikko is a traditional Finnish sweetened potato casserole, where mashed potatoes are gently “malted” to develop natural sweetness, then baked low and slow with milk and butter. The result is a softly caramelised, mildly sweet side dish that’s essential on Finnish Christmas tables and pairs perfectly with ham, turkey or other festive mains.
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Prep Time 45 minutes
Cook Time 10 hours
Total Time 10 hours 45 minutes
Servings: 6 people
Course: Side Dish
Cuisine: Finnish
Calories: 330
Ingredients Method

Ingredients
  

  • 2 kg (4 lbs) starchy potatoes the starchier the better
  • 2 dl (¾ cup) all-purpose flour
  • 50 g butter (plus a little extra for greasing and dotting on top)
  • ½ - 1 l (2-4 cups) whole milk, warmed
  • 2-3 tsp fine salt
  • ½ tsp ground nutmeg or white pepper (optional, for mild spice)
  • 1-2 tbsp dark syrup (only if needed!)

Method
 

Step 1 – Cook and Mash the Potatoes
  1. Peel the potatoes and cut into chunks of roughly equal size.
  2. Place in a large pot, cover with unsalted water and boil until very tender.
  3. Drain well, reserving a little of the cooking water if you like for adjusting consistency.
  4. Mash until completely smooth – a potato ricer is ideal for a silky casserole.
  5. You want a soft mash, but not too runny. Add a splash of the cooking water if it seems dry.
Step 2 – Start the Sweetening
  1. Let the mash cool down a little until it’s warm but not hot – ideally around 50 °C / 122 °F.
  2. Stir in half of the flour (1 dl) and about half of the butter, cut into small pieces.
  3. Mix thoroughly, then sprinkle the remaining flour on top of the mash without stirring it in completely – this gives the enzymes a good contact layer.
Step 3 – Let It Sweeten (The “Imellytys” Phase)
  1. Cover the pot with a lid.
  2. Keep the mash warm (roughly 50–65 °C / 122–149 °F) for 4–8 hours.
  3. If you have a thermometer, check occasionally to make sure it doesn’t climb much above 70 °C / 158 °F.
  4. Over time, the mash will become looser and noticeably sweeter and more mellow in flavour. The top may darken slightly where the flour sat – that’s normal.
Step 4 – Season and Loosen the Mash
  1. Once you’re happy with the sweetness, stir the mash thoroughly so any flour on top is fully mixed in.
  2. Warm the milk and melt the rest of the butter.
  3. Add milk gradually, stirring, until the mash is softer than normal mashed potatoes, but not soupy – think thick cake batter.
  4. Season with salt and nutmeg/white pepper (if using).
  5. Taste. If the sweetening hasn’t developed enough, add 1–2 tbsp dark syrup and stir well. The flavour should be gently sweet, not dessert-level sugar bomb.
Step 5 – Bake Low and Slow
  1. Preheat the oven to 150 °C / 300 °F.
  2. Grease one large or two medium casserole dishes with butter.
  3. Pour the potato mixture into the dishes, leaving some headspace – the casserole will bubble and puff a little.
  4. Dot the surface with a few small bits of butter. You can also draw a simple pattern with a spoon or fork for the classic Finnish look.
  5. Bake for 2–3 hours, until the top is deep golden brown, the edges have caramelised a bit and the casserole feels set in the centre..
  6. Let it rest at least 15 minutes before serving so it firms up slightly.