Hollandaise breaks when egg yolks and fat separate, which happens because you've exceeded the emulsion's threshold. An emulsion is simply tiny fat droplets suspended in water, held together by lecithin in the egg yolk. Push the temperature too high or add fat too quickly, and you overwhelm that delicate balance. The Cold Water Fix If your hollandaise splits into greasy pools, stop immediately and start a new bowl with a single egg yolk at room temperature. Add your broken sauce one tablespoon at a time, whisking constantly, as though you're starting fresh. The new yolk's lecithin will re-emulsify the separated fat. This method works roughly 80% of the time. Prevention is simpler: keep your bowl over gently simmering water (not touching the water), add clarified butter slowly—literally one teaspoon at a time for the first quarter cup—and maintain a constant, gentle whisking motion. Professional chefs rarely make hollandaise over direct heat anymore; the double boiler method gives you precious control. Temperature should never exceed 160°F, or your yolks will scramble instead of emulsify.