Melt the chocolate chips with 1 Tbsp butter in a double boiler over simmering water until smooth. Alternately, melt In a microwave safe bowl in the microwave. Use the melt function or heat in 20 second increments, stopping to stir each time. Repeat until smooth.
In a small bowl, whisk together the sugar, cornstarch and salt. Whisk beaten yolks into cornstarch-sugar mixture until fully combined. The mixture will be thick.
Meanwhile, Add half and half and remaining 2 Tbsp butter to a heavy bottomed saucepan. Cook over medium-high heat until the butter has melted and the half and half is hot, don't boil.
Whisk the sugar-egg mixture into the half and half then bring to a boil. Immediately, lower the temperature to medium to prevent scorching, whisking constantly for 1 minute after thickened.
Remove from the heat and whisk in the melted chocolate and vanilla. Pour into a glass bowl, and press plastic wrap directly on top of the chocolate custard to prevent a film from forming. Chill for 2 hours.
To assemble in a 3 or 4 quart bowl start with a layer of vanilla wafers. Top with 1/3 sliced bananas then 1/3 chocolate custard. Repeat, vanilla wafers, banana slices and chocolate custard.
Next, spread 2 cups whipped cream. Top whipped cream with a layer of vanilla wafers and banana slices. May line the side of the bowl with standing wafers, if desired. Top with final 1/3 custard.
Chill for at least 4 hours. Frost with remaining whipped cream and sprinkle with grated chocolate just before serving.
If you choose to make this in a 13 x 9 inch dish, you will reduce the vanilla wafer, chocolate custard and banana layers to 2 instead of 3 as pictured. Use all of the whipped cream on top.