Begin by scrubbing your potatoes and placing them in an oven set to 200C. Bake on a rack for 45 minutes or until completely tender and cooked through.
Pierce with a knife until the tip reaches the centre. If the knife goes in easily and the tip of the knife comes out warm, you’re good to go. If there is resistance then cook for 15 more minutes.
While these are cooking, place the milk, garlic and thyme in a small pot over medium high heat. Don’t take your eyes off the pot for more than a few seconds at a time, milk loves to boil over.
Cut each cured fish fillet into 2 pieces if it doesn’t fit easily in the pot.
Once the milk comes up to a simmer, add the cured fish and stir. Turn off the heat and allow the fish to poach for 8 minutes or until the fish is flakey and tender.
Remove the pot from the stove and strain out the milk into a mixing bowl. Reserve the milk to adjust the consistency of the brandade later
Remove the skin from the fish and allow the fish to cool while you finish the potatoes.
Once the potatoes are cooked, cut them in half and scoop out the flesh with a spoon. Place the flesh into a mixing bowl and reserve the skins for other uses (back into the oven with some oil and salt until crispy for potato skins)
Using a potato masher or fork, crush the potatoes well.
Place the cooked fish into the bottom of a clean pot and top with 100ml or so of the fish milk.
Break up the fish into smaller flakes with a spoon or spatula. Add the mashed potato to the pot and stir to combine. Bring the pot up to medium heat.
Add milk as necessary until the mixture comes together and takes on the consistency of your ideal mashed potatoes. Once everything is warmed through and combined, taste for seasoning and add more salt if necessary.
To finish, add plenty of chopped dill and the zest from half of a lemon and a tablespoon or so of juice, adjusted to your tastes. Adjust the salt one last time and serve nice and hot. Alternatively, spoon into a baking dish and grill in the oven until the top is browned and crunchy to enjoy as a meal.