To make butterscotch sauce, melt the butter in a medium saucepan. Add brown sugar and stir until melted.
Stir in the heavy cream and bring to a boil. Boil for 3 minutes. Remove from heat and stir in vanilla. Pour into a bowl and let cool to room temperature.
Preheat oven to 350 degrees and spray a tube pan or bundt pan with baking spray with flour.
Whisk together the flour, baking powder, baking soda, and salt in a medium bowl. Set aside.
Add melted butter to a large bowl. Whisk in 1 cup of packed light brown sugar and vanilla extract.
Whisk in 2/3 cup butterscotch sauce.
Whisk in eggs one at a time.
Stir in half the flour mixture, then the sour cream, followed by the remaining flour mixture.
Pour half the batter into the prepared pan.
In a small bowl, mix together the pecans, remaining 1/2 cup brown sugar, and the cinnamon.Sprinkle half the mixture over the batter in the prepared pan.
Pour the remaining batter into the pan, using a spatula to spread it evenly.Sprinkle remaining pecan mixture on top.
Bake for 40 to 45 minutes. Check after 30 minutes and tent pan with foil if at risk of getting too brown on top.
Let cool in pan for 15 minutes and then remove from pan and place on serving plate.