It is the starch which causes thickening kheer recipe. But there are few ways to thicken the pudding. 1. You can add 1 tbsp corn starch with 1/4 cup of water and add in the kheer while cooking. This will thicken the kheer. 2. Adding 1/2cup-1cup condensed milk will result in thick pudding. Adjust sugar after adding it. 3. Simmer the pudding for longer time will also make a thick pudding.