Preheat the oven to 180°C (350°F). Place the Lutefisk in a shallow, ovenproof dish and season lightly with Coarse salt and a little Ground white pepper. Dot the top with small pieces of Unsalted butter, cover tightly with foil and bake until the fish is hot and flakes easily, about 15–25 minutes depending on thickness.
While the fish is baking, wash and place the Waxy potatoes in a pot of cold water, bring to a boil, and simmer until just tender when pierced, about 15–20 minutes. Drain and keep covered to stay warm.
Fry the Streaky bacon in a skillet over medium heat until crisp. Remove the bacon to a paper towel to drain and chop or crumble when cool; reserve about 1–2 tablespoons of the bacon fat in the pan.
In the same skillet with the reserved bacon fat, add another knob of the unsalted butter and cook gently until it foams and takes on a light golden, nutty aroma—this quick brown-butter mixture will add richness to the fish. Keep warm but do not let it burn.
Heat the Green peas briefly in simmering water or a microwave until just cooked and bright green, then drain and season with a pinch of salt and a grind of pepper.
To assemble, transfer portions of the baked lutefisk and the warm potatoes to plates. Spoon the brown-butter and bacon-fat sauce over the fish, scatter the chopped crisp bacon over everything, and add a spoonful of Strong mustard to the side.
Serve immediately with Flatbrød on the side for crunch—tear a piece and use it to scoop the fish, potatoes, and mustard for an authentic finish.
