Place the baking tray in the preheated oven (electric range: 225 °C/ convection oven: 200 °C/ gas: level 4) on the middle shelf. Place baking paper on top and spread the fish fingers. Bake for 13-15 minutes.
Bring 175 ml of water to the boil in a saucepan. Add vegetables, bring to the boil over high heat, cover and cook for about 3 minutes. Remove the pot from the heat, let it cool down for 1 minute without lid. Stir in the puree briefly with a wooden spoon.
Arrange the puree with the fish fingers and tartar sauce. Garnish with chervil.