Preheat oven to 350°F (175°C). Mix graham cracker crumbs, melted butter, and 3 tablespoons sugar in a bowl until the texture resembles wet sand. Press firmly into the bottom and up the sides of a 9-inch pie pan. Bake for 10 minutes until golden and fragrant, then cool completely on a wire rack.

In a medium saucepan, whisk together 3/4 cup sugar, cornstarch, and salt. Gradually whisk in the milk until smooth with no lumps visible. Cook over medium heat, whisking constantly, until the mixture thickens and begins to bubble, about 8-10 minutes.

Remove from heat. Whisk 1/2 cup of the hot milk mixture into the beaten egg yolks to temper them, then pour the egg mixture back into the saucepan. Return to medium heat and cook, whisking constantly, for 2 minutes until very thick and pudding-like.

Remove from heat and stir in 2 tablespoons butter and 1 1/2 teaspoons vanilla until the butter melts completely. Press plastic wrap directly onto the surface of the custard and refrigerate for 30 minutes until slightly cooled but still spreadable.

Arrange half of the sliced bananas in an even layer over the cooled crust. Pour half of the custard over the bananas and spread gently. Layer the remaining bananas on top, then cover with the remaining custard, smoothing the surface. Refrigerate for at least 3 hours or overnight until fully set.

Just before serving, beat cold heavy cream, powdered sugar, and 1 teaspoon vanilla in a chilled bowl with an electric mixer on medium-high speed until stiff peaks form, about 3-4 minutes. Spread or pipe the whipped cream over the chilled custard layer.

Slice with a sharp knife dipped in hot water and wiped clean between cuts. Garnish with additional banana slices or a sprinkle of cinnamon if desired. Serve immediately for the best texture and presentation.