Coat an 8-inch square pan with butter or non-stick spray. Stage the sugar, cinnamon, and vanilla, and marshmallows so they are ready to add quickly.
This can be made in the microwave or on the stovetop. Either method: on low, gradual heat, melt the butter in a large container.
Once the butter is melted, remove from heat and stir in the brown sugar, cinnamon and vanilla. Add marshmallows and stir to melt. The hot butter should melt the marshmallows, but if needed give it an extra zap in the microwave or briefly heat on low on the stovetop. Stir until no white streaks remain.
Remove from heat again, if needed. Add in the cinnamon cereal and 1/4 teaspoon salt. As soon as everything is coated, pour it into the prepared pan. Quickly spread it to the corners and evenly press it down. Sprinkle more coarse salt and turbinado sugar on top.
Let the pan cool for at least 15 minutes before slicing and serving.
!OM NOM NOM!