Preheat the oven to 190 °C (375 °F) conventional oven (top and bottom heat).
Scrub the 4 waxy potatoes well and slice them, skin on, into paper-thin slices.
Line a baking sheet with parchment paper and lay the potato slices on it.
Halve 3 cloves garlic lengthwise, skin on, and add them to the potatoes.
Add 2 tsp olive oil, salt and a little pepper to the potatoes and spread everything thoroughly with your fingers.
Spread the potatoes out on the sheet as thinly as possible and drizzle with the remaining 2 tsp olive oil.
Put the sheet in the oven and pre-bake for about 5 min.
Meanwhile, pat 500 g salmon fillet with skin dry and remove any remaining bones if necessary.
Salt the salmon and, after the 5 minutes, place it skin side up on the potatoes. Lay 3 sprigs of thyme on the skin and let the salmon finish cooking in about 15 - 20 min. (see Tips & Tricks)
Take out the salmon and, if you like, brown the potatoes a little more under the oven broiler until extra crispy.
Before serving, remove the skin from the salmon if you like.
To serve, either arrange the salmon and potatoes on a large platter or divide them into 2 portions. Sprinkle with a little salt & pepper and fresh thyme leaves and enjoy.