In a large bowl, combine warm water, active dry yeast, and sugar. Allow to sit for 5-10 minutes until frothy. Add olive oil and salt, then gradually add the flour to form a dough. Knead for about 5-7 minutes until smooth. Cover and let it rise for 1 hour in a warm place.

Preheat Oven

Preheat your oven to 475°F (245°C) while the dough is rising.

Prepare the Cheese Filling

In a bowl, mix the Fontina cheese, Feta cheese, chopped chives, and Za'atar spice blend until well combined.

Shape the Khachapuri

Once the dough has risen, punch it down and divide it into 2 equal portions. Roll each portion into a circle about 10 inches in diameter. Place the cheese filling in the center and fold the edges over to create a boat shape.

Add Egg Yolk

Create a small well in the center of each filled boat and carefully add an egg yolk. Sprinkle with red chili flakes.

Bake

Transfer the Khachapuri to a baking sheet lined with parchment paper and bake for 15-20 minutes until the crust is golden brown and the cheese is bubbling.

Serve

Remove from the oven, let cool slightly, and serve warm, optionally with additional Za'atar on top.