Prepare the Cake:
Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl, cream the butter and sugar until light and fluffy. Add eggs one at a time, beating well after each addition. Stir in vanilla extract.
Gradually add the dry ingredients, alternating with buttermilk, beginning and ending with the dry ingredients. Mix until just combined.
Divide the batter evenly between the prepared pans and bake for 30–35 minutes, or until a toothpick inserted into the center comes out clean.
Let the cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.
Make the Caramel Sauce:
In a saucepan over medium heat, melt the sugar while stirring continuously until it turns a golden brown.
Add the butter and stir until melted. Gradually add the heavy cream and salt, stirring constantly.
Allow the caramel sauce to cool before using.
Toast the Walnuts:
Preheat a skillet over medium heat. Add chopped walnuts and toast for 2–3 minutes, stirring frequently, until fragrant.
Assemble the Cake:
Place one cake layer on a serving plate. Spread a thin layer of whipped cream or cream cheese frosting over the top.
Arrange mango slices and sprinkle with toasted walnuts. Drizzle caramel sauce over the mango and walnuts.
Place the second cake layer on top and repeat the process with the frosting, mango, walnuts, and caramel sauce.
Decorate the Cake:
Frost the sides of the cake with whipped cream or cream cheese frosting, if desired.
Garnish with additional mango slices, walnuts, and a drizzle of caramel sauce for a beautiful finish.
Chill and Serve:
Refrigerate the cake for at least 1 hour before slicing to allow the flavors to meld.