Traditionally, Imeruli and Suluguni cheese are used, which are difficult to find abroad. An ideal substitute is a mixture of Mozzarella, Feta, and Ricotta/Cottage, which creates the correct texture—meltable but salty. Khachapuri is eaten by tearing off a piece of bread and dipping it into the mixture of hot butter and raw yolk.
In a small bowl, mix the warm milk/water, yeast, and sugar. Let it activate for 10 minutes.
In a large bowl, mix the flour and salt. Add the active yeast, oil, and knead into a smooth, elastic dough. Cover the dough and let it proof in a warm place for 60-90 minutes until it doubles in volume.
Grate the cheese. If using different types, mix them. Add 2 tbsp of milk (or 1 egg white) and mix. The filling should be moist but not runny.
Divide the proofed dough into 4 parts. Roll each part into an oval.
On the longer side, roll the oval inwards towards the center from both sides to form the edges of the 'boat'. Pinch the ends to create a pointed shape. This forms the boat-shaped space for the filling.
Preheat the oven to a high temperature, 230 °C (445 °F).
Evenly distribute the cheese mixture and fill the center of each boat. Brush the edges with the beaten egg.
Bake for 10-12 minutes, or until the bread is golden brown and the cheese is bubbly and lightly browned.
Remove the Khachapuri from the oven. Use a spoon to make a well in the centre of the cheese filling and place one raw egg yolk and a piece of butter into each.
Return to the oven for 1-2 minutes. The yolk should remain runny, and the butter should start to melt.
Serve immediately. It should be eaten by tearing off a piece of bread and dipping it into the mixture of hot butter and raw yolk.