To make the cake: Follow the recipe for the Old Fashioned Butter Cake. This can be done a day or two in advance of assembling your Boston Cream Layer Cake. Wrap cooled layers in plastic wrap and refrigerate.
To make the custard: In a small bowl, mix together the sugar, cornstarch and salt.
Separate the egg yolks from the egg whites. Reserve the egg whites for another recipe or freeze.
Whip the egg yolks together then into the sugar mixture.
Add the half and half and butter to a heavy bottomed saucepan. Heat over medium-high heat until the butter has melted.
Whisk the sugar-egg mixture into the hot half and half and bring to a boil. Whisk constantly for 1-2 minutes or until thickened.
Remove from the heat and add the vanilla.
Pour into a bowl, and press plastic wrap on top. Chill completely.
To assemble the cake: Remove the custard from the fridge and use a fork or whisk to mix until creamy and smooth.
Center one cake round on a serving plate. Top with ½ of the pastry cream.
Place the second round on top of the pastry cream and repeat.
Place the final round on top.
Chill the cake until set.
To frost: Melt the chocolate chips together with the cream until smooth. Melt in a double boiler, or in the microwave in 20 second increments stopping to stir each time. Cool until slightly warm to the touch and the thickness of a pourable pudding.