Preheat the oven to 180°C (350°F) and position the grill at the center of the oven. Butter and line the bottom of two 20-cm (8-inch) square baking dishes with parchment paper, allowing it to hang over two sides. Place the dishes on a cookie sheet.
To make the butterscotch caramel sauce, combine the sugar, Scotch, water, and syrup in a saucepan and bring to a boil. Cook without stirring until the mixture takes on a golden color. Remove from heat and gradually add the hot cream and butter. Bring to a boil again while stirring until the mixture is smooth. Divide the caramel into the two baking dishes and sprinkle half of the pecans over the caramel.
In a separate bowl, combine the flour, chopped pecans, baking soda, and salt. Set aside.
In another bowl, use an electric blender to cream the butter with the oil, brown sugar, and vanilla. Add the eggs, one at a time, beating until the mixture is smooth and homogeneous. At low speed, add the dry ingredients alternately with the buttermilk. Carefully divide the batter into the two baking dishes over the caramel.
Bake for about 50 minutes, or until the cakes are fully cooked. Allow them to cool for approximately 30 minutes.
Invert one of the cakes onto a serving platter. Invert the second cake onto a baking sheet and slide it onto the first cake. Let cool completely.
Serve the cake warm or cold and top with whipped cream if desired.