Instructions: 1. Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking dish.
2. Prepare the Cake Batter: Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, beginning and ending with the dry ingredients. Mix until just combined.
3. Prepare the Pie Filling: Cook over medium heat, stirring frequently, until the mixture thickens and the mangoes are softened, about 5-7 minutes.
4. Assemble the Cake: Spoon the remaining cake batter over the mango pie filling, spreading it out as evenly as possible.
5. Make the Streusel Topping: In a small bowl, mix together the flour, granulated sugar, brown sugar, and cinnamon. Cut in the cold butter using a pastry cutter or fork until the mixture resembles coarse crumbs.
BAKE and Serve: Bake in the preheated oven for 40-45 minutes, or until the cake is golden brown and a toothpick inserted into the center comes out clean.Serve warm or at room temperature, optionally with a dollop of whipped cream or a scoop of vanilla ice cream.