Both methods can be used to make curds. The "direct heat" method makes you cook the curd directly inside the saucepan on a very low heat. It is the quickest method, but you risk overcooking the curd and the eggs. The "indirect heat" method requires you to cook the curd in a heat-proof bowl over a double-boiler. It takes much longer to thicken, but you avoid the risk of burning the curd.