Grate the onion and squeeze out a little of its juice.
Combine 300 g ground beef, the onion, 3 tbsp rice, washed, 1 egg, 1 heaped tbsp flour, plus more for dusting, 1 tsp salt and 1 tsp black pepper; knead until smooth and firm.
Roll into small meatballs, about the size of a marble.
Dust the meatballs with flour and shake off the excess.
Heat 1 spoon of butter with olive oil in the pot; sauté 1 dessert spoon of flour.
Stir in 1 dessert spoon of tomato paste.
Add the carrots and sauté 5 minutes.
Pour in water to past halfway up the pot; salt it.
Once boiling, add a quarter of the lemon.
Add the meatballs and the potatoes; cook about 20 minutes.
Make the terbiye: whisk 1 egg yolk, for the terbiye with the juice of half a lemon, then whisk in 5–6 spoonfuls of the hot soup.
Stir the terbiye into the pot and cook 10 minutes more.
Notes
The meatball mix below is written for this soup — mom had already made her meatballs when she sent the recipe.
Dust the meatballs with flour; it helps the soup thicken.
Don't skip tempering the terbiye — it keeps the yolk from curdling.