1. Prepare Oven and Pans:

• Preheat your oven to 350°F (175°C).
• Grease and flour two 9-inch round cake pans. Lining the bottoms with parchment paper is also recommended.

2. Cream Butter and Sugar:

• In a large mixing bowl, using an electric mixer (stand or handheld), cream together the softened butter and granulated sugar until light and fluffy (about 3-4 minutes).

3. Add Eggs and Flavorings:

• Beat in the room temperature eggs one at a time, ensuring each is fully incorporated before adding the next. Scrape down the bowl as needed.
• Stir in the melted (and slightly cooled) butterscotch chips and vanilla extract until well mixed.

4. Combine Dry Ingredients:

• In a separate medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt.

5. Alternate Dry and Wet Ingredients:

• With the mixer on low speed, gradually add the dry mixture and the room temperature buttermilk to the butter mixture, beginning and ending with the dry ingredients (add dry in 3 parts, buttermilk in 2 parts). Mix only until just combined after each addition. Do not overmix.

6. Bake the Cakes:

• Divide the batter evenly between the two prepared cake pans. Smooth the tops with a spatula.
• Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center of the cakes comes out clean.
• Allow the cakes to cool in the pans on wire racks for about 10 minutes.
• Carefully invert the cakes onto the wire racks to cool completely.

7. Make the Crunch Topping:

• While the cakes cool (or earlier), make the topping. Combine the chopped pecans, crushed pretzels, packed brown sugar, and melted butter in a small bowl. Stir well.
• Spread this mixture evenly onto a baking sheet (lined with parchment if desired).
• Bake at 350°F (175°C) for 8-10 minutes, or until golden brown and fragrant. Watch carefully to prevent burning.
• Allow the crunch topping to cool completely on the baking sheet. Break up any large clumps once cooled.

8. Make the Butterscotch Frosting:

• Ensure the butter is properly softened and the butterscotch sauce is at room temperature.
• In a large bowl using an electric mixer, beat the softened butter until creamy.
• Gradually add the sifted powdered sugar, alternating with the butterscotch sauce and heavy cream. Beat on low speed initially, then increase speed until the frosting is light, fluffy, and well combined.
• Stir in the vanilla extract. Beat again briefly. If frosting is too thick, add a tiny bit more cream; if too thin, add more sifted powdered sugar.

9. Assemble the Cake:

• Ensure cake layers are completely cool. If desired, level the tops with a serrated knife.
• Place one cake layer on your serving plate or cake stand.
• Spread a generous layer of the butterscotch frosting over the top (about half of the frosting).
• Place the second cake layer on top.
• Use the remaining frosting to frost the top and sides of the cake smoothly or decoratively.

10. Add Crunch Topping:

• Sprinkle the cooled crunch topping generously over the top of the frosted cake.
• Gently press some of the crunch topping onto the sides of the cake as well, if desired.

11. Chill Before Serving:

• Chill the cake in the refrigerator for at least 30 minutes before slicing. This allows the frosting to set slightly, making slicing easier.

12. Serve:

• Slice and serve the cake. It’s best enjoyed closer to room temperature.