Step 1: Cook the onion
Heat the oil in a saucepan over medium heat. Add the chopped onion and cook until soft and golden. Stir in the turmeric and black pepper.
Step 2: Prepare the kashk
Whisk the kashk with 2 cups of water in a bowl until smooth. Break up any lumps before adding it to the saucepan.
Step 3: Add the seasonings
Stir the flour into the cooked onions, followed by the dried mint and chopped walnuts. Cook briefly, stirring to prevent the mint from burning.
Step 4: Add the kashk mixture
Reduce the heat and gradually pour in the diluted kashk while stirring continuously until the ingredients are well combined.
Step 5: Simmer the dish
Simmer gently for about 20 minutes, stirring occasionally. Adjust the consistency with a little hot water if needed, and taste before adding salt.
Step 6: Serve warm
Transfer the Kaleh Joosh to serving bowls. Garnish with extra mint or walnuts if desired, and serve warm with fresh Persian flatbread.