Preheat oven to 300. Lightly grease 6 ramekins or custard cups with butter. Set ramekins in a rectangular oven-safe casserole dish.
Scald milk by cooking on medium heat, stirring frequently to prevent a skin from forming, just until bubbling. Remove from heat and set aside to cool.
Blend eggs, vanilla, sugar, and salt in a blender. When milk has reached 110 degrees F, add to blending ingredients until thoroughly mixed.
Pull out the oven's middle rack and set casserole dish with ramekins on it. Pour warm water into the casserole dish until ramekins are about 1/3 covered. Pour egg and milk mixture into ramekins, distributing evenly until almost completely full. Bake 40 minutes.