Heat milk, sugar, and salt in a saucepan on medium heat for about 5 minutes, stirring occasionally.
Whisk the cream and cornstarch in a small bowl until very smooth.
Whisk the cream/cornstarch mixture into the heated milk and cook until the mixture starts to simmer.
Reduce heat to low and stir constantly, for 5 minutes until the pudding is thickened.
Remove pan from heat and stir in butter and banana extract until butter has melted. Transfer pudding to a bowl to cool.
Mix graham crackers (less 1 teaspoon for an optional garnish), cinnamon, and melted butter in small bowl. Transfer to a 10-ounce ramekin and press the mixture evenly in the bottom (the bottom of a measuring cup or drinking glass works well for this).
Layer sliced bananas (reserve one for a garnish) on top of the graham cracker crust and pour the banana pudding over the bananas.
Cover the pie with plastic wrap and chill up to 2 hours.
Top with whipped cream, banana slices, and graham cracker crumbs.