Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a bowl, mix together the flour, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl, beat the softened butter, granulated sugar, and light brown sugar until creamy.
Add eggs one at a time, beating well after each addition, then mix in the vanilla extract.
Gradually add the flour mixture to the batter, alternating with buttermilk. Begin and end with the flour mixture. Mix until just combined.
Divide the batter evenly between the prepared cake pans.
Bake in the preheated oven for 25-30 minutes or until a toothpick inserted into the center comes out clean.
Let the cakes cool in the pans for 10 minutes, then turn them out onto a wire rack to cool completely.
Once the cakes are cooled, spread the caramel sauce evenly over the top of both cakes. Stack them if desired.