Whisk together egg yolks, 1/4 cup sugar, cornstarch, salt, and vanilla. Set aside.
In a medium saucepan over medium heat, steep together coconut milk, whole milk, shredded coconut, and 1 cup of sugar. Whisking occasionaly, bring to boil.
Once boiling, remove from heat and temper into egg yolks. I like to start with about a 1/2 cup of the milk mixture and, in a slow and steady stream, whisk into the egg yolks. Continue to do this 3 more times making sure to keep the egg yolks moving so they don't scramble. Pour egg yolk and milk mixture back into the pot with remaining milk. Return to heat.
Whisk mixture on medium low heat until mixture begins to thicken and bubble. Remove from heat and stir in butter.
Pour mixture into baked and cooled pie crust. Cover with plastic wrap directly on top of coconut filling to prevent a skin from forming. Chill until cooled and set. This can take 3-4 hours minimum.