Step 1: Make the Cake Layers
Preheat your oven to 350°F. Grease and line two 9-inch round cake pans.
In a medium bowl, whisk together flour, baking powder, baking soda, and salt. In a large bowl, cream butter and sugar until light and fluffy, about 3–4 minutes. Beat in eggs one at a time, then add vanilla. Alternate adding the dry ingredients and buttermilk, beginning and ending with the flour mixture.
Divide the batter evenly into prepared pans and bake for 25–30 minutes, or until a toothpick comes out clean. Let cool completely on wire racks.

Step 2: Prepare the Caramel Frosting
In a large saucepan, melt butter over medium heat. Add brown sugar and stir until dissolved. Slowly pour in evaporated milk while stirring. Bring to a gentle boil, then reduce heat and simmer for 3–5 minutes. Remove from heat and stir in vanilla.
Let the mixture cool slightly, then gradually beat in sifted powdered sugar until desired consistency is reached. The frosting should be thick but spreadable. If it gets too stiff, add a splash of milk.

Step 3: Assemble the Cake
Place one cake layer on a serving plate. Spread a thick layer of caramel frosting on top. Add the second cake layer and frost the top and sides of the cake. Work quickly, as the frosting sets fast. Garnish with a drizzle of warm caramel, sea salt flakes, or crushed toffee if desired.

Step 4: Let It Set
Allow the cake to sit at room temperature for at least 30 minutes before slicing. This helps the frosting firm up and gives you those clean, glossy edges.