Boil the milk and let cool. If you want to cool it quicker, place the bowl with milk in a bigger one, filled with cold water, keep it there for a while, then change the water for 2-3 times.
Notice that in the video recipe I skipped this step and it didn't make any difference. So, it's up to you if you boil the milk or not - besides, the one in the shops is already pasteurized anyway.