Tanabour (Armenian Yogurt and Barley Soup)

 Melt 2 tablespoons butter in large saucepan over medium heat. Add onion, mint, salt, pepper, and baking soda. Cook, stirring occasionally, until onion has broken down into soft paste and is just starting to stick to saucepan, 6 to 8 minutes.

 Stir in barley. Cook, stirring frequently, until grains are translucent around edges, about 3 minutes. Add broth and water. Increase heat to high and bring to boil. Adjust heat to maintain gentle simmer; cook, partially covered, until barley is very tender, 50 minutes to 1 hour, stirring occasionally. Meanwhile, whisk yogurt and egg yolk together in large bowl.

 Remove saucepan from heat. Whisking vigorously, gradually add 2 cups barley mixture to yogurt mixture. Stirring constantly, add yogurt-barley mixture back to saucepan. Cover and let sit for 10 minutes to thicken.

 Heat soup over medium heat, stirring occasionally, until temperature registers between 180 and 185 degrees (do not allow soup to boil or yogurt will curdle). Remove from heat. Soup should have consistency of buttermilk; if thicker, adjust by adding hot water, 2 tablespoons at a time. Stir in 2 tablespoons cilantro and season with salt to taste.

 Melt remaining 2 tablespoons butter in small skillet over medium-high heat. Off heat, stir in Aleppo pepper. Ladle soup into bowls, drizzle each portion with 1 teaspoon spiced butter, sprinkle with remaining 2 tablespoons cilantro, and serve. (Leftovers can be refrigerated for up to 3 days; reheat gently, being careful not to allow temperature to exceed 180 degrees. If necessary, thin by adding water, 2 tablespoons at a time.)