In a medium saucepan, whisk together: ¾ cup granulated sugar,¼ cup cornstarch, ½ teaspoon salt.
In a separate bowl, whisk together: 1 ½ cups whole milk,1 ½ cups heavy cream, 5 large egg yolks & 1/2 tablespoon vanilla extract.
Slowly whisk the milk mixture into the sugar mixture. Cook over medium heat, stirring constantly, until it thickens to a pudding-like consistency. Keep the heat at medium to avoid cooking the pastry cream too quickly or preventing it from thickening properly.
Once thickened, remove from heat and strain into a large bowl.
Stir in: 4 tablespoons unsalted butter (one tablespoon at a time)
Let the pastry cream cool for 15 minutes, stirring occasionally. Cover with plastic wrap directly on the surface and refrigerate until chilled (about 90 minutes). After the pastry cream has chilled in the fridge, it's time to whip up the whipped cream and assemble the cake.