Step 1: Preheat your oven to 425°F (220°C) to prepare for the crust.
Step 2: Place the refrigerated pie crust in the pie dish, press into place, poke holes, and bake for 10-12 minutes until golden. Cool completely.
Step 3: In a saucepan, mix whole milk, brown sugar, cornstarch, cinnamon, nutmeg, and salt, whisking until smooth.
Step 4: Whisk egg yolks until creamy, then gradually add warm milk mixture to temper the eggs.
Step 5: Return egg mixture to saucepan, cook over medium heat until thickened and boiling, about 5-7 minutes. Remove from heat, and stir in butter and vanilla.
Step 6: Slice bananas and layer over the cooled pie crust.
Step 7: Pour custard over bananas, smooth the top, and let cool at room temperature for 30 minutes. Refrigerate for at least 2 hours until set.
Step 8: Whip heavy cream, powdered sugar, sour cream, and vanilla until soft peaks form.
Step 9: Spread whipped cream over the chilled pie, creating peaks.
Step 10: Slice and serve chilled. Enjoy!