Let’s build this caramel dream cake step-by-step:

1. Prepare Pans and Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans, then line the bottoms with parchment paper.

2. Make the Cake Batter:

• In a large bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
• In another large bowl (or stand mixer bowl), beat the softened butter and granulated sugar until light and fluffy, about 3-4 minutes.
• Add the eggs, one at a time, beating well after each addition. Stir in the vanilla extract.
• Alternate adding the dry ingredients and the buttermilk to the butter mixture, starting and ending with the dry ingredients. Mix on low speed just until combined after each addition. Do not overmix.

3. Bake the Cakes:

• Divide the batter evenly between the prepared cake pans. Smooth the tops with a spatula.
• Bake 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 transfer them carefully to a wire rack to cool completely.

4. Make the Caramel Sauce:

• In a medium saucepan, heat the granulated sugar over medium heat, stirring constantly with a heatproof spatula or wooden spoon. The sugar will clump, then melt, and eventually turn an amber liquid color. Watch carefully to prevent burning.
• Once the sugar is melted and amber, carefully stir in the cubed butter until fully melted. Be cautious as it may sputter.
• Slowly and carefully pour in the heavy cream while continuing to stir. The mixture will bubble vigorously.
• Add the pinch of salt and continue cooking and stirring for 1-2 minutes until the sauce is smooth.
• Remove from heat and let cool slightly. It will thicken as it cools. Reserve 1/4 cup for the frosting; set the rest aside for filling/drizzling.

5. Prepare the Frosting:

• In a large bowl (or stand mixer bowl), beat the softened butter until creamy.
• Gradually add the powdered sugar, beating on low speed until incorporated, then increasing speed until smooth.
• Add the reserved 1/4 cup of cooled caramel sauce and the vanilla extract. Continue beating until combined.
• Add heavy cream, one tablespoon at a time, beating until the frosting reaches a smooth and spreadable consistency.

6. Assemble the Cake:

• Level the cooled cake layers if necessary. Place one cake layer on your cake stand or serving plate.
• Spread a generous layer of caramel buttercream frosting over the top.
• Drizzle with a little extra caramel sauce (from the portion set aside earlier).
• Sprinkle evenly with about half of the crushed toffee pieces and pecans (if using).
• Place the second layer of cake gently on top.
• Frost the top and sides of the cake smoothly with the remaining caramel buttercream.

7. Add the Final Touch:

• Decorate the top and/or sides of the cake with the remaining crushed toffee pieces and pecans.
• Drizzle generously with the remaining caramel sauce for that stunning, glossy finish. Chill briefly to help set the drizzle if desired.

Patience with the caramel sauce is key!