1. Preheat and Prepare: Preheat your oven to 350°F (175°C). Grease and flour a 9×13 inch baking pan. Alternatively, grease two 8-inch or 9-inch round cake pans and line the bottoms with parchment paper, then grease and flour the sides.
2. Combine Dry Ingredients: In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, light brown sugar, baking soda, baking powder, salt, and pumpkin pie spice. Ensure there are no clumps, especially in the brown sugar.
3. Combine Wet Ingredients: In a separate medium bowl, whisk together the pumpkin puree, vegetable oil, lightly beaten eggs, buttermilk, and vanilla extract until well combined and smooth.
4. Combine Wet and Dry: Pour the wet ingredient mixture into the large bowl containing the dry ingredients. Using a rubber spatula or wooden spoon, mix gently until just combined. Be very careful not to overmix; a few small streaks of flour remaining are okay at this stage. Overmixing develops the gluten too much, leading to a tougher cake.
5. Fold in Chocolate: Add the chocolate chips or chunks to the batter. Gently fold them in until they are evenly distributed throughout the batter. Again, minimize mixing strokes.
6. Pour and Spread: Pour the batter into the prepared baking pan(s). If using round pans, divide the batter evenly between them. Gently spread the batter evenly using an offset spatula or the back of a spoon.
7. Bake: Place the pan(s) in the preheated oven.

   • For a 9×13 inch pan, bake for approximately 35-45 minutes.
   • For 8-inch or 9-inch round pans, bake for approximately 30-40 minutes.
   • Bake until the top springs back lightly when touched and a wooden skewer or toothpick inserted into the center comes out clean (a few melted chocolate streaks are fine, but no wet batter).

8. Cool Completely (Crucial Step): Remove the cake(s) from the oven and place the pan(s) on a wire cooling rack. Let the cake cool in the pan(s) for at least 20-30 minutes. If using round pans, carefully invert them onto the wire rack, peel off the parchment paper, and let them cool completely, right side up. For a 9×13 pan, let it cool completely in the pan on the wire rack. Allow the cake to cool 100% before attempting to frost it. This can take 2-3 hours at room temperature. Warm cake will melt the frosting into a greasy mess.

Part 2: Making the Dreamy Butterscotch Frosting

1. Make Butterscotch Base: In a medium saucepan, melt the unsalted butter over medium heat. Once melted, stir in the dark brown sugar and the pinch of salt. Bring the mixture to a gentle boil, stirring constantly. Continue to boil gently for 2-3 minutes, still stirring, until the sugar is dissolved and the mixture slightly thickens and looks glossy (like a thin caramel sauce).
2. Add Cream: Carefully and slowly pour the heavy cream into the boiling brown sugar mixture while whisking constantly. Be cautious as it will bubble up vigorously. Continue whisking and let it bubble gently for another 30-60 seconds.
3. Cool Butterscotch Base: Remove the saucepan from the heat. Pour the hot butterscotch mixture into a heatproof bowl (preferably the bowl of your stand mixer or a large mixing bowl if using a hand mixer). Let this mixture cool completely to room temperature. This step is vital! If the base is warm, it will melt the powdered sugar and result in runny frosting. Cooling can take 30-60 minutes; you can speed it up slightly by placing the bowl in the fridge for short bursts, stirring occasionally, but don’t let it solidify completely. It should be thick but still fluid at room temperature.
4. Beat the Frosting: Once the butterscotch base is completely cool, add the sifted powdered sugar (start with 2 ½ cups) and the vanilla extract to the bowl. Using an electric mixer (stand mixer with paddle attachment or hand mixer), beat on low speed initially to incorporate the sugar, then increase to medium-high speed. Beat for 3-5 minutes until the frosting is light, fluffy, and smooth.
5. Adjust Consistency: Check the frosting consistency. If it’s too thin, add more sifted powdered sugar, a few tablespoons at a time, beating well after each addition, until it reaches a thick, spreadable consistency. If it’s too thick, add a splash more heavy cream or milk (1 teaspoon at a time), beating until smooth.

Part 3: Assembling the Cake

1. Frost the Cake: Ensure your cake is COMPLETELY cool.

   • For 9×13 pan: Dollop the butterscotch frosting over the top of the cooled cake directly in the pan. Use an offset spatula or knife to spread it evenly.
   • For Layer Cake: Place one cake layer on your serving plate or cake stand. Spread about 1/3 to 1/2 of the frosting evenly over the top. Carefully place the second cake layer on top. Spread the remaining frosting over the top and sides of the cake, smoothing as desired.

2. Garnish (Optional): If desired, gently warm a little extra butterscotch sauce (store-bought or homemade) and drizzle it over the frosted cake. Sprinkle with toasted chopped pecans or walnuts, flaky sea salt, or even mini chocolate chips.
3. Set (Optional): You can let the cake sit for about 30 minutes before slicing to allow the frosting to set slightly, especially if making a layer cake.
4. Slice and Serve: Use a sharp knife (wiping it clean between slices helps for neatness) to cut and serve. Enjoy!