Place the unopened can of sweetened condensed milk in a large pan. Cover with water. Simmer over medium-high heat for 3 hours, adding more water as needed to keep the can covered at all times. Remove can from the hot water using tongs and let cool completely.
Preheat the oven to 350 degrees F (175 degrees C).
Combine almond flour, salt, and baking soda in a large bowl. Whisk melted butter, agave nectar, and vanilla extract together in a small bowl. Stir into the almond flour mixture until thoroughly combined. Press into a deep-dish pie pan.
Bake in the preheated oven until golden brown, 12 to 15 minutes. Let cool completely.
Meanwhile, whisk milk and egg yolks together in a bowl. Combine sugar, cornstarch, and salt in a large saucepan. Pour in milk mixture and stir until thoroughly combined. Add vanilla bean halves to the pan. Cook over medium heat, stirring constantly, until custard is thick and glossy, about 10 minutes. Remove from heat. Discard vanilla bean. Cool the custard for 30 minutes.
Open the can of cooked sweetened condensed milk and pour 1/2 over the pie crust. Spread evenly. Cover evenly with sliced bananas. Pour cooled custard over the bananas. Refrigerate pie for 2 hours. Place a bowl and beaters in the refrigerator for the icing.
Make icing before serving the pie. Sprinkle gelatin over cold water in a microwave-safe bowl; let soften for 5 minutes. Dissolve gelatin in the microwave for 3 minutes, stirring after every minute. Let cool until still liquid but no longer warm, about 10 minutes.
Pour heavy cream into the chilled bowl. Beat at high speed until beaters leave clear trails. Slowly add sugar and vanilla extract. Continue beating, pouring in gelatin in a steady stream, until stiff peaks form. Spoon over the pie. Serve immediately or refrigerate.