Step 1: Prepare the oven and pans
Preheat your oven to 350°F (175°C).
Grease and flour two 9-inch round cake pans thoroughly.
Make sure to tap out any excess flour for a clean finish.

Step 2: Cream the butter and sugar
In a large mixing bowl, cream together the softened butter and granulated sugar.
Beat for about 3-4 minutes until the mixture becomes light, fluffy, and pale in color.
This step is key for creating a tender crumb.

Step 3: Add the eggs
Beat in the eggs one at a time, making sure each one is fully incorporated before adding the next.
This helps to emulsify the batter and create a stable structure.
Scrape down the bowl as needed to ensure even mixing.

Step 4: Add melted butterscotch and vanilla
Stir in the melted butterscotch chips and vanilla extract until the mixture is smooth and uniform.
The butterscotch will add rich, caramelized flavor throughout the cake.
Be sure the butterscotch is melted but not piping hot when adding.

Step 5: Mix dry ingredients
In a separate bowl, whisk together the flour, baking powder, baking soda, and salt.
Whisking helps to distribute the leaveners evenly.
Set aside for use shortly.

Step 6: Alternate dry ingredients and buttermilk
Gradually add the dry mixture to the butter mixture, alternating with the buttermilk.
Begin and end with the dry ingredients, mixing just until combined after each addition.
Avoid overmixing to keep the cake tender.

Step 7: Bake the cakes
Divide the batter evenly between the two prepared pans.
Smooth the tops gently with a spatula.
Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.

Step 8: Cool the cakes
Let the cakes cool in the pans for about 10 minutes after baking.
Then, carefully turn them out onto wire racks to cool completely.
Cooling is crucial before frosting to prevent melting.

Step 9: Prepare the frosting
Beat the softened butter in a large bowl until creamy.
Gradually add the powdered sugar, alternating with the butterscotch sauce and heavy cream.
Beat until the frosting is light, fluffy, and spreadable.

Step 10: Make the crunch topping
In a small bowl, combine the chopped pecans, crushed pretzels, brown sugar, and melted butter.
Spread the mixture onto a parchment-lined baking sheet.
Bake at 350°F for 8-10 minutes until golden brown, then let cool completely.

Step 11: Assemble the cake
Spread a generous layer of butterscotch frosting on top of one cake layer.
Place the second cake layer on top and frost the top and sides.
Use an offset spatula for smooth coverage.

Step 12: Add the crunch topping
Sprinkle the cooled crunch topping over the frosted cake.
Press gently so that it sticks to the frosting.
Chill the cake for at least 30 minutes before slicing for clean cuts.