Lightly spray a 9×13-inch pan with nonstick spray and set aside.
In a large pot over low heat, melt the butter and dissolve the salt.
Add the mini marshmallows and stir until completely melted and smooth. Remove from the heat.
Stir in the vanilla extract. Then fold in the Rice Krispies until evenly coated.
Transfer the mixture to the prepared pan. Use lightly buttered or damp hands to gently press the treats into an even layer. Don’t compact them, or the bars will turn dense.
Let cool for 1 hour, then cut into 16 squares.
Spread red frosting diagonally across the top corner of each treat to form the Santa hat.
Transfer the white frosting to a piping bag fitted with a star tip. Pipe a row of stars along the bottom edge of the red frosting.
Press a mini marshmallow onto the top corner to create the pom-pom.