Stir together the brown sugar and cinnamon in a medium-sized bowl. Then add the softened butter (NOT melted****) and vanilla extract, then stir until evenly mixed.
¾ cup light brown sugar, 1 ½ tablespoon ground cinnamon***, ⅔ cup salted butter, ½ teaspoon vanilla extract
Using a rolling pin, roll the dough into a large rectangle, about 20x15 inches (size doesn't matter much here--but keep in mind that the wider the rectangle, the taller your cinnamon rolls will be, and the taller the rectangle, the more spiral your cinnamon rolls will have).
Evenly spread the filling on the rolled out dough, covering it completely.
The easiest way to shape the cinnamon rolls is to cut the dough into 12 strips using a pizza cutter, and then roll each strip into a spiral. If you'd like to roll the entire rectangle of dough and then slice into individual rolls with a knife or unflavored floss, that works too. Use cooking spray to oil your glass 13x9 pan. Evenly place each spiral into the pan, tucking the end piece under the spiral (this keeps them tucked nicely while baking).
Cover with a cloth and let rise to double.