Preheat your oven to 350°F (175°C). Grease and line a rectangular baking pan with parchment paper.

In a bowl, whisk together the flour, baking powder, and salt. Set aside.

In a separate large bowl, beat the sugar and eggs together until pale and fluffy. This might take about 5 minutes. Mix in the vanilla extract.

Gradually add the dry ingredients to the egg mixture, folding gently until just combined. Be careful not to overmix.

Pour the batter into the prepared baking pan and smooth the top with a spatula. Bake in the preheated oven for 20-25 minutes or until a toothpick inserted into the center comes out clean.

While the cake is baking, prepare the chocolate buttercream. In a bowl, beat the softened butter until creamy. Gradually add the powdered sugar, cocoa powder, and vanilla extract, mixing until smooth and well combined. Set aside.

Once the cake is done, remove it from the oven and let it cool in the pan for a few minutes. Then, transfer it to a wire rack to cool completely.

While the cake is cooling, prepare the caramel topping. In a small saucepan, combine the granulated sugar and water over medium heat. Stir until the sugar dissolves, then let it simmer without stirring until it turns a golden amber color. Remove from heat and let it cool for a few minutes until it thickens slightly.

Once the cake has cooled, carefully slice it into several rectangular layers of equal thickness.

Spread a generous amount of chocolate buttercream between each layer, stacking them on top of each other.

Pour the caramel topping over the assembled cake, spreading it evenly with a spatula. Allow it to cool and harden before serving.