For the bechamel sauce, froth 40g butter in a pan. You shouldn't get a tan. Then sprinkle with the flour and stir into a dough-like mass. Now stir in the cold milk with the whisk until all of the flour has dissolved. Add a little salt, a little pepper and grated nutmeg and simmer for about 30 minutes. Stir frequently so that the sauce doesn't burn to the bottom. Pour the sauce through a sieve and season again with salt, pepper and nutmeg.
Peel and quarter the potatoes. Bring to a boil in a saucepan with salted (one teaspoon) water and cook on a low flame. Peel the asparagus and place in another saucepan with lightly salted water. Add half of the well washed lemon, a teaspoon of sugar and 20g of butter. Also cook the asparagus on a low flame. It shouldn't get too soft. Therefore always check with the tip of a knife.
Rinse the barramundi fillet and pat dry well with paper towels. Incise the skin in a diamond shape. Salt and pepper the fillets on both sides. 2 tbsp. Heat the oil in the pan. Fry the fillets on the skin. Press the fillet firmly with the turner for the first 15 seconds, then it does not bulge. After 2-3 minutes, turn the fillet and fry from the second side until the middle is no longer translucent.
Now arrange the plates. Place the asparagus and potatoes on top. Pour the bechamel sauce over it and the fried barramundi fillet on top. Finally, sprinkle the plates with chopped parsley.