In a large, light-colored saucepan, melt the butter over medium heat.
Continue cooking until golden while stirring or swirling the contents of the pan. The butter will foam, then turn golden brown and smell nutty. This will take about 6-8 minutes.
Add in the marshmallows and stir until almost melted.
Add in sugar cookie mix and stir until combined.
Remove from heat and stir in rice cereal.
While still warm, stir in the sprinkles. Don’t overmix — you want to still see the festive red and green colors.
Pour into prepared dish and let cool.
Notes
Browning the butter will give a caramel flavor. If you would like the sugar cookie flavor to stand out more, just melt the butter instead of browning it.