Perch En Papillote

Peel and finely dice potatoes. Cook potatoes in salted boiling water until very al dente, about 5 minutes. Drain.

Preheat the oven to 200°C (approximately 400°F). Rinse, trim and cut leek into 5-cm (approximately 2-inch) long pieces. Peel and finely dice carrots. Brush chanterelles thoroughly to remove dirt. Melt butter in a frying pan. Add vegetables, mushrooms and potatoes and cook briefly. Mix in approximately 1 teaspoon horseradish. Season with salt and pepper. Rinse thyme, shake dry, and strip the leaves from two sprigs. Mix thyme leaves into vegetables. Prepare four double-folded sheets of parchment paper. Divide vegetables among parchment pieces. Rinse fish fillets and pat dry. Season fish with salt and pepper and sprinkle with a little lemon juice. Place fish on vegetables, skin-side up. Top with thyme sprigs. Fold packets over and crimp to seal. Place packets on a baking sheet and bake 25-30 minutes.