Preheat oven to 350°F (175°C). Grease or line a 9x13-inch pan with parchment paper.

In a bowl, mix flour, granulated sugar, and powdered sugar.

Cut in the cold butter until the mixture resembles coarse crumbs.

Press evenly into the prepared pan and bake for 12-15 minutes until the edges are pale gold.

Mash bananas until smooth with small lumps.

In a saucepan, whisk together milk, cream, eggs, granulated sugar, cornstarch, vanilla, and salt.

Cook over medium-low heat, whisking constantly, until thickened.

Remove from heat and stir in mashed bananas.

Pour banana filling over the hot crust and spread evenly.

Bake for 18-22 minutes until slightly jiggly in the center and edges are puffed.

Let bars cool at room temperature for 30 minutes, then cover and chill in the fridge for at least 3 hours.

Run a knife under hot water, dry it, and cut the bars into squares.

Add optional toppings if desired.