Preheat the oven to 350°F. Spray three 8-inch cake pans with baking nonstick spray. Line the bottoms of the cake pans with 8-inch parchment paper circles and spray again.
In a medium bowl, mix the flour, baking powder, baking soda, and salt. Set aside.
3 ½ cups All-purpose flour, 2 teaspoon Baking powder, 1 teaspoon Baking soda, 1 teaspoon Salt
In a large bowl, using a mixer, beat the butter and brown sugar on high speed for 3 minutes. Add in the vanilla and butterscotch sauce. Mix on medium until combined. Add the eggs one a time and mix until just combined.
1 cup Unsalted butter, 1 ½ cups Brown sugar, 1 teaspoon Pure vanilla extract, ½ cup Butterscotch sauce, 4 Large eggs
Add ⅓rd of the dry ingredients and half of the buttermilk and mix on low speed. Mix until they just start combining before adding the next. Add another ⅓rd of the dry ingredients and the rest of the buttermilk. Finish with the rest of the dry ingredients.
1 cup Buttermilk
Pour the cake batter evenly into each cake pan. Bake for 24-28 minutes. Bake until a toothpick inserted comes out clean.
Let the cakes sit in the hot pans for 10 minutes. Transfer the cakes onto a cooling rack. Cool completely.