• Line a half-sheet baking pan with plastic wrap, ensuring the sides of the pan are also covered. Set aside.
• In a large bowl, whisk together cornstarch, about ½ cup of sugar, and cocoa powder. Add in egg yolks and about ½ cup of milk. Whisk until smooth. Set aside.
• Pour remaining milk into a heavy bottomed sauce pot. Add remaining sugar. Set over medium-high heat. Stir occasionally to ensure the milk does not burn along the sides or bottom of the pan.
• When the milk has boiled, slowly add about ¼ cup of hot milk into the egg mixture. Whisk constantly to distribute the heat. Continue to pour more milk until a couple tablespoons are left in the saucepan. Then pour the egg-milk mixture back into the saucepan.
• Reduce to medium heat. Switch to a spatula. Stir constantly until the custard has thickened. To cook the cornstarch out, heat the custard until it boils for about 10-15 seconds. Remove from heat.
• Stir in butter, chocolate chips, and salt until smooth.
• Pour pastry cream into a plastic wrapped sheet pan. Spread evenly. Cover surface directly with plastic wrap and freeze for 15 minutes* until pastry cream has cooled to room temperature
• Remove from freezer. Transfer to another container. Cover surface directly with plastic wrap. Keep chilled in the fridge until ready to use.

Revive Chilled Pastry Cream:

• Remove from fridge. Place in a large mixing bowl. Loosen the chilled pastry cream using a sturdy whisk. Or, place in a stand mixer and beat with whisk or paddle attachment. (Also works with beaters of an electric hand mixer.) Beat until smooth and creamy.