Heat milk, vanilla seeds, and salt in pan and bring to boil.

In large mixing bowl, whisk sugar and cornstarch and eggs until smooth. Slowly add 1/2 milk mixture into egg mixture and whisk constantly to temper them. Add remaining milk and return the whole thing to saucepan.

Cook until consistency is thick, whisking nonstop.

Remove from heat and pour into a bowl, letting it cool for 10 min, then incorporate butter a little at a time until smooth.

Cover the surface with plastic wrap, directly touching cream, and let it cool in refrigerator.