Lightly spray a 9×13-inch pan with nonstick spray and set aside.
In a small bowl, whisk together the sugar and cinnamon. Set aside.
In a large pot over low heat, melt the butter and dissolve the salt.
Stir in the cinnamon and cream of tartar and cook for about 30 seconds until fragrant.
Add 14 ounces of the mini marshmallows and stir until completely melted and smooth.
Remove from the heat. Stir in the vanilla extract.
Fold in the Rice Krispies cereal and the remaining 2 ounces of mini marshmallows until evenly coated.
Transfer the mixture to the prepared pan and gently press into an even layer. Avoid packing the treats too firmly.
Sprinkle the cinnamon-sugar mixture evenly over the top.
Let cool for 1 hour before cutting into 16 squares.