Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans or line them with parchment paper. In a large bowl, cream together butter, brown sugar, and granulated sugar until light and fluffy. Beat in the eggs one at a time, followed by molasses and vanilla extract.

In a separate bowl, whisk together flour, baking powder, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, alternating with buttermilk, beginning and ending with the dry ingredients. Mix just until combined.

Divide the batter evenly between the prepared pans. Bake for 25–30 minutes, or until a toothpick inserted in the center comes out clean. Let cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely. In a saucepan over medium heat, melt the butter.

Add brown sugar and milk. Stir constantly until the sugar dissolves and the mixture begins to boil. Let it boil gently for 2–3 minutes, then remove from heat. Stir in heavy cream, vanilla extract, and a pinch of salt. Let it cool slightly before frosting.

Once cakes are completely cool, spread a layer of frosting over one cake round. Place the second cake layer on top, and frost the top and sides evenly with the caramel frosting.