Preheat the oven to 180°C.
Wash the potatoes thoroughly and cut them into smaller pieces. Transfer them to a baking sheet, add olive oil, thyme, and salt. Toss everything together. Roast for about 30–35 minutes, until golden and crispy.
Add the peas to salted boiling water and cook for about 6–8 minutes. Drain and rinse with cold water to preserve their vibrant colour. Use a food processor or blender to puree the peas with butter, milk, and salt until smooth.
Wash and pat dry the cod fillets. Place them in a baking dish, season with salt, pepper, and chopped dill on both sides. Top with small pieces of butter. Bake covered for 15–24 minutes at 180°C, depending on the thickness of the fillets. Check the fish a few minutes before the end – if it’s ready, you can remove it, otherwise, bake for a little longer. Enjoy your meal!