Line a quarter-sheet baking pan with plastic wrap, making sure the sides of the pans are covered. Set aside.
Pour coconut cream and ¾ cup milk into a large heavy bottomed sauce pot. Whisk together and place over medium heat. Stir occasionally to ensure milk does not burn along sides or bottom of pot. Bring to a simmer.
Meanwhile, in a medium bowl, whisk together sugar and cornstarch. Add in remaining ¼ cup milk and eggs. Whisk until smooth.
Once milk is at a simmer, reduce heat. Slowly add about ⅓ cup of hot milk mixture into cornstarch mixture. Whisk constantly to distribute heat. Continue to add milk and whisk until only about ⅓ of milk is left into sauce pot.
Pour all of cornstarch-milk mixture back into the sauce pot. Increase to medium heat. Whisk constantly until mixture has thickened to a custard. Allow mixture to come to a boil for 15-30 seconds to cook out any cornstarch flavor. Remove from heat.
Whisk in butter until smooth. Add in salt and vanilla and whisk until combined.
Pour hot pastry cream into prepared plastic wrapped sheet pan. Spread evenly. Cover with surface of pastry cream directly with plastic wrap. Freeze for 10-15 minutes until pastry cream has cooled to room temperature. Remove from the freezer and transfer pastry cream to an airtight container. Place plastic wrap directly on surface of pastry cream. Cover with lid. Let chill in the fridge until ready to use.