This is caused by too much heat and suggests the custard has been overcooked or cooked without the use of a bain-marie, or the oven temperature was too high. Any of these could result in pitting, so producing some moisture around the edges, and it cannot be rectified. Check your oven temperature, and use a bain-marie. The simmering water around the dish lowers the temperature, ensuring a lower, even temperature during cooking.
** Asian Recipes