Finely crumble the rusk (works well if you work it with a rolling pin in a closed freezer bag) and mix with the mustard and oil. Salt and pepper the fish fillets on both sides.
Line a baking sheet with parchment paper, drizzle some olive oil on it, place the fish fillets on the baking sheet and spread evenly with the mustard crust. Bake at 200 ° top heat for about 15 minutes.
For the puree, peel the potatoes, cut them into small pieces and cook for approx. 20 minutes in boiling salted water.
Finely chop the olives and the clove of garlic.
When the potatoes are cooked, drain them off. Heat the milk in the saucepan and season with salt and pepper. Add the potatoes, olives and garlic to the milk and mash to a creamy puree.
Serve the fish fillet with the mashed potatoes. A green salad or cucumber salad goes well with it.
Tip: You should start with the preparation of the puree, as the potatoes take longer to cook than the fish.