In the city center of Sofia, around Vitosha Boulevard, you will find a large choice of restaurants. It is a very lively neighborhood and if you start to stroll in the small surrounding streets, you will discover several nice family restaurants, with more reasonable prices and a warm welcome. This is how I got to test Agarta that I recommend to you.
For 20Lv (10 €), you can taste a very fresh grilled trout cooked in the Mediterranean way
They produce their own lemonade at 3.9Lv (2 €) which is very refreshing after a good ride!
They also bake their own cakes every day. 4.5Lv (€ 2.25) per piece of cake
By metro, get off at NDK station (National Palace of Culture) M2.
One of the waiters speaks English, and their menu is written in Bulgarian and English. I highly recommend it !