Make the base: Heat the oven to 350°F. Grease an 8-inch square pan and line it with parchment paper so that the paper comes up higher than the edge of the pan on all sides. In a medium bowl, add the flour, pecans, and salt and mix briefly to combine. Add the melted butter and stir until a thick paste-like dough forms. Press the dough into a flat layer on the bottom of the parchment-lined pan. Prick the dough all over with the tines of a fork and bake for 18 to 20 minutes or until golden brown. Let cool completely before assembling. Spread the shredded coconut into an even layer on a lined sheet pan and bake for 3 to 5 minutes or until lightly browned. Repeat with the pecans and bake for 8 to 10 minutes or until darkened and fragrant. Make the vanilla pudding: In a medium saucepan, combine the egg yolks, sugar, cornstarch, and salt and whisk until the mixture becomes thick and pale. Slowly stream in the half-and-half, whisking all the while. Place the pan over medium heat and whisk frequently until the mixture begins to steam. At this stage, whisk the pudding constantly until it becomes very thick and begins to bubble. Let the pudding boil for 1 minute, whisking all the while, before transferring to a wide, shallow dish. Whisk in the butter and vanilla extract and spread the pudding into an even layer. Cover with plastic wrap pressed directly onto the surface of the pudding and chill for 30 minutes to 1 hour, or until cold. To assemble, give the chilled pudding a good stir with a spatula to smooth it out before spreading it into an even layer over the pecan base. Arrange the banana slices in a single layer on top of the pudding. Set aside. In a large mixing bowl, combine the heavy whipping cream, sour cream, and powdered sugar, and whisk until the mixture holds firm peaks. Spread into an even layer over the banana slices. Scatter the top of the whipped cream with the toasted coconut and arrange the pecans evenly on top. Cover and let chill for at least 2 hours and up to a day before serving. Store leftovers in an airtight container in the refrigerator for 2 to 3 days.