Khoya is an ingredient used in Indian desserts and not eaten by itself. This recipes is more about the technique since the only ingredient is milk. The milk is reduced over a low heat until you have just the solids remaining. Milk should be full fat and the pan should be thick bottomed and nonstick. You can make any amount of this you want, I suggest 6 cups so you have to proper amount to use in tomorrows recipe. Six cups makes almost a cup of khoya.
6 cups 4 % milk
Place the milk in a deep pan with a thick bottom, preferable nonstick. Turn the heat to medium low and cook stirring until the mixture thickens. This process takes 60 - 90 minutes of fairly frequent stirring. I suggest Netflix.
At first it will just look like milk in a pan. Be careful through all of this to keep stirring so it doesn't scorch on the bottom, milk tends to.
Next it will look like parts are starting to clump up and get thick. Just keep stirring, just keep stirring, anyone else picturing Dory?
Past that stage, and after about at least an hour the milk will start to be really thick and the bubbles will look like when a pancake needs to be flipped. At this point make sure and stir really well. It will hold together in one mass and you will be able to see the bottom of the pan.
Cook and stir until it is thick enough to flip. Remove from the heat and remove from the pan. As it cools it will thicken up even more, at this point it should be solid enough to grate.
Store in the fridge. It should stay good for 2-3 days chilled.