Preheat the oven to 350°F (175°C). Grease a 10- to 12-cup Bundt pan well and sprinkle the pecans in the bottom, if using.
Shake the sugar and cinnamon together in a gallon zip-top bag.
Quarter each biscuit, shake the pieces in the cinnamon sugar in batches and layer loosely in the pan.
Melt the butter, brown sugar and leftover cinnamon sugar over medium heat. Boil 1 minute, then stir in the vanilla and salt.
Pour over the biscuits. Bake on a rimmed sheet 35–40 minutes, until deep golden and the center is cooked (about 190°F).
Cool in the pan 10 minutes, then invert onto a plate and serve warm.