Blanch the chard in boiling hot salted water, then remove the coarse leaf veins. Cut the pike perch into 4 even pieces, season lightly with salt and season with pepper.
Wrap 1 pike-perch piece in each of 2 chard leaves. Place on a buttered baking sheet and form 1 butter flake on top of each.
Cook in the oven at 120 degrees for 10 minutes. Ideal alternative: steam in a steamer or in a saucepan with a sieve insert.
In the meantime, cook fish stock, Noilly Prat, double cream and saffron until creamy. Season with a dash of sugar, juice of one lemon, salt and white pepper. Serve the pike-perch in chard leaves with the sauce.