They bake for about 20-25 minutes. The trick is to pull them when the tops are uniformly golden brown, the edges are just starting to pull away from the liners, and the centers have only the slightest jiggle when you gently shake the pan. I learned the hard way that overbaking makes the custard layer firm and rubbery instead of soft and creamy. I let them cool in the tin on a rack for at least 20 minutes. They will sink slightly in the center as they cool—this is normal and creates the perfect little well for a dusting of powdered sugar.
Pro Tips for Best Results
For the most dramatic “impossible” separation and the creamiest custard base, make sure your blender batter is completely smooth and your oven is fully preheated. I tested this three different ways (hand-whisking, using cold ingredients, and using the blender with room-temp ingredients), and the blender method with room-temperature dairy gave by far the best layered result.
Let the melted butter cool for a few minutes before adding it to the blender. If it’s piping hot, it can start to cook the eggs when you blend, creating little curdled bits. You want it liquid, but just warm to the touch.
Resist the urge to open the oven door during the first 15 minutes of baking. The sudden temperature drop can disrupt the delicate separation process. Use the oven light to check on their progress until the final few minutes.(See the next page below to continue…)