Poached Cod in Peppery Tomato Sauce

Ingredients

• 1 tbsp unsalted butter
• 1 small yellow onion (finely chopped)
• 4 garlic cloves (minced)
• 1 tbsp green peppercorns (drained, roughly chopped)
• ½ tsp salt
• ½ tsp sugar
• 1 tsp black pepper
• 1 tsp dried thyme
• 2 tbsp double concentrated tomato paste
• 1 ¾ cups puréed tomatoes
• 4 cod fillets
• a pinch of flaky salt
• ¼ tsp chili flakes (for serving)
• 1 tbsp chopped parsley (for serving)