Soup-e Mast (سوپ ماست) — Persian Spiced Yogurt Soup

• 500 gPlain yogurt (full-fat, unsweetened) (room temperature for easier tempering)
• 30 gAll-purpose flour (about 1/4 cup, leveled)
• 900 mlWater (divided)
• 1 largeEgg yolk (optional but helps prevent curdling)
• 7 gFine sea salt (about 1 1/4 tsp, plus more to taste)
• 30 gUnsalted butter (or ghee)
• 12 gGarlic (4 cloves, finely grated or minced)
• 10 gFresh ginger (finely grated)
• 60 gFresh green peppers (1–2 mild green chilies, deseeded if desired, thinly sliced)
• 2 tspGround cumin
• 1 tspGround turmeric
• 1 tspCurry powder (use a mild blend)
• 0.5 tspBlack pepper (freshly ground)
• 20 gFresh coriander (cilantro) (finely chopped, plus extra for serving)
• 15 mlLemon juice (about 1 tbsp, optional for extra tang)

Instructions

1. 1

   Prepare the yogurt base: in a bowl, whisk the yogurt, flour, egg yolk (if using), salt, and 300 ml of the water until completely smooth with no flour lumps. Let it stand 5 minutes at room temperature; this hydrates the flour and helps the soup thicken evenly without a raw flour taste.

2. 2

   Build the aromatic foundation: set a medium pot over medium heat and melt the butter (about 1 minute). Add garlic, ginger, and sliced green peppers and cook 2–3 minutes, stirring, until fragrant but not browned. Add cumin, turmeric, curry powder, and black pepper; toast 30–45 seconds to bloom the spices.

3. 3

   Simmer the broth: pour in the remaining 600 ml water and bring to a gentle simmer over medium-high heat (about 4–6 minutes). Reduce heat to low and simmer 5 minutes so the spices infuse the liquid. Keep the pot at a low simmer, not a rolling boil, to prevent the yogurt from splitting later.

4. 4

   Temper and combine: while whisking the yogurt mixture constantly, ladle in 200 ml of the hot spiced liquid in a slow stream (about 1 minute). Then pour the warmed yogurt mixture back into the pot, whisking continuously. Keep heat on low and cook 10–12 minutes, stirring often, until velvety and lightly thickened.

5. 5

   Finish and serve: stir in chopped cilantro and cook 1 minute. Taste and adjust salt and pepper; for brighter tang, add lemon juice off the heat. Rest the soup 5 minutes to settle, then serve warm (not boiling hot), garnished with extra cilantro and a few slices of green pepper if desired.