Make The Banana Custard

• In a large mixing bowl, whisk together the egg yolks, banana puree, sugar, cornstarch and salt until smooth and thoroughly combined.
• In a medium saucepan heat the milk, cream, rum and vanilla over medium-high heat until steaming but not bubbling. Reduce the heat to the lowest setting.
• While whisking the egg yolk mixture, gradually pour in about half of the hot milk mixture to temper the egg yolks. (I like to start with 2-3 tablespoons of hot milk first and whisking vigorously to prevent the eggs from curdling).
• Pour the tempered egg mixture into the saucepan with the remaining milk mixture and cook over medium-low heat for 5-7 minutes until the mixture becomes thick and has a custard like texture (coats the back of a wooden spoon and drops off easily but isn't runny).
• Remove the saucepan from heat and beat in the cold butter. 
• Pour the custard into a large bowl and allow to cool for a few minutes.
• Cover the surface of the custard with plastic wrap to prevent a skin from forming, and chill in the refrigerator for 4 hours or up to two days (any longer and the bananas will turn the custard brown).
• Divide mixture into four ramekins. Smooth the tops with the back of a spoon for an even surface.
• Cover the surface of the custards with a generous layer of turbinado sugar. Lightly pat the sugar down with the back of a spoon.
• Using a kitchen torch, broil the sugar for 30 seconds - 1 minute until the sugar is fully caramelized and resembles glass. Alternatively, you can set your oven to 500F (260 C) and broil the custards on the top rack for 2 minutes until caramelized and bubbly.
• Serve immediately, or if making in advance, wait to add the sugar and broil until right before serving.