Preheat the oven to 350°F (175°C). Grease a 9x5-inch loaf pan or similar baking dish and line the bottom with parchment if desired.
Tear the Vietnamese-style baguette into roughly 1-inch pieces and spread them on a baking sheet; toast in the oven for 8–10 minutes until lightly crisped and golden. Transfer to the prepared pan in an even layer.
In a large skillet over medium heat, melt 2 tablespoons of Unsalted butter with 2 tablespoons of Granulated sugar until bubbling and caramel-colored. Add sliced Bananas and cook 1–2 minutes per side just to caramelize — you want them softened but not falling apart. Arrange the caramelized bananas over the toasted bread in the pan.
In a mixing bowl, whisk together 3 large Eggs and 1/2 cup of Granulated sugar until smooth. Add 1 cup of Coconut milk, 1/3 cup of Sweetened condensed milk, 2 tablespoons of melted Unsalted butter, 1 teaspoon of Vanilla extract, and 1 tablespoon of Dark rum; whisk until combined.
Whisk in a pinch of Salt and 2 tablespoons of All-purpose flour (sifted if you like) to slightly thicken the custard. Taste and adjust sweetness if needed.
Pour the custard mixture evenly over the bread and banana layers, pressing gently so the bread soaks up the liquid. Let the dish rest 10–15 minutes to allow the bread to absorb the custard.
Bake in the preheated oven for 40–50 minutes, until the top is golden and a skewer inserted near the center comes out mostly clean with a few moist crumbs. If the top browns too quickly, tent loosely with foil.
Remove from the oven and let cool at least 15–20 minutes to set. Serve warm or at room temperature, plain or with a drizzle of extra coconut milk or condensed milk if desired.
