Step 1: Prepare the Mango Filling

Start by peeling and cutting the mangoes into small chunks. If the mangoes are very ripe, they will release more juice, which enhances the sweetness of the filling. Place the mango chunks in a mixing bowl and add granulated sugar. The amount of sugar can be adjusted based on how sweet the mangoes are. Stir in the corn starch, which helps thicken the filling and prevents excess moisture from making the pastry soggy. Mix well and set the bowl aside while preparing the crumb mixture.

Step 2: Make the Crumb Mixture

In a large mixing bowl, combine the flour, baking powder, and salt. Mix well to distribute the ingredients evenly. Add the cold, cubed butter into the dry ingredients. If using a food processor, pulse the mixture until small crumbs form. If working by hand, use a pastry cutter or two forks to cut the butter into the flour mixture until it resembles coarse crumbs. Keeping the butter cold is important, as it ensures a flaky texture in the pastry.

In a separate bowl, whisk together the brown sugar, egg, and vanilla extract. Pour the wet ingredients into the crumbly flour mixture and mix until combined. The mixture should remain slightly crumbly but hold together when pressed.

Step 3: Assemble the Layers

Line an 8×8-inch baking pan with parchment paper to prevent sticking and make it easier to lift the bars out after baking. Take about two-thirds of the crumb mixture and press it firmly into the bottom of the pan to create an even base layer. Ensure that the layer is packed tightly to provide a sturdy foundation for the mango filling.

Evenly spread the prepared mango filling over the crumb base. Use a spatula to distribute it so that every bite has a good balance of pastry and mango. Sprinkle the remaining crumb mixture over the top, making sure to cover the mango filling as much as possible.

Step 4: Bake the Mango Crumb Bars

Preheat the oven to 350°F (175°C). Place the baking pan in the oven and bake for 35-40 minutes, or until the top is golden brown. The filling should be bubbling slightly, indicating that it has thickened properly.

Once baked, remove the pan from the oven and allow the bars to cool for 5-10 minutes. Carefully lift the parchment paper and transfer the bars to a cooling rack. Let them cool for another 15-20 minutes before slicing into nine equal squares.