Traditionally, Urum is made from yak milk, which has an extremely high-fat content. At home, we can use full-fat cow's milk, ideally with added cream for better yield and thickness.
A crucial part of the process is 'samrach' - scooping the milk with a ladle and pouring it back into the pot from a height. This helps foam the milk and evenly distribute the fat, which is essential for creating a thick top layer.
In a wide-bottomed pot (ideally cast iron or heavy-bottomed), combine the milk and heavy cream.
Heat over medium heat until the milk reaches just below boiling point (let it simmer gently but not vigorously boil). The ideal temperature is 85 °C to 90 °C (185 °F to 195 °F).
Once the milk reaches the desired temperature, start performing 'samrach': use a ladle to scoop up the milk from the bottom and pour it back onto the surface from a height (approx. 10-15 cm / 4-6 in).
Repeat this motion continuously for 30-45 minutes. The goal is to create a stable and thick layer of foam on the surface that becomes saturated with fat. Reduce the heat to the minimum, so the milk is just gently simmering.
Turn off the heat. Carefully move the pot to a cool place and leave it undisturbed.
The Urum layer will start to form as the milk cools. The pot must not be moved or opened during this process.
Allow to cool for 12 to 18 hours (traditionally overnight).
After the cooling period, a thick, yellowish-white layer of Urum will have formed on the milk's surface.
Carefully use a sharp knife to cut around the edges of the Urum layer.
Use a large, wide spoon or spatula. Gently lift the Urum layer, which can be slightly rolled up or transferred to a plate as a thick sheet. The remaining skimmed milk can be processed further or drunk.
Serve Urum immediately, traditionally with fresh Boortsog and/or sprinkled with sugar or served with honey. It is also often stirred into hot Suutei Tsai (milk tea).