Begin melting butter in a large saucepan set over low heat.
Toss in the marshmallows.
Continue to stir, occasionally, until about 75% of the marshmallows have melted.
Remove the pan from the heat and continue to stir, smashing the marshmallows, until they melt completely.
Stir in the cake batter flavoring.
Pour the cereal into a large, well buttered mixing bowl.
Pour the marshmallows over top and stir to fully incorporate.
Stir in 3 tablespoons of the sprinkles just until combined.
Gently spread into a well buttered 8-inch or 9-inch pan.
Toss the remaining 1 tablespoon of sprinkles over top.
Press down on the top of the cereal treats to ensure the sprinkles are secure.
Allow the treats to cool at least 30 minutes before cutting into 16 squares .
Notes
Microwave Method:
Heat butter and marshmallows on high power for 1 minute.
Remove and stir.
If needed, heat for 15-30 second increments, stirring vigorously after each, until melted.
Add the cake batter flavoring then pour over the cereal and continue using the instructions above.
Store:
Store in an airtight container at room temperature for up to 5 days .
Wrap well in non-stick tin foil or wax paper, then over-wrap in a zip-top bag and freeze for up to 3 months. Thaw at room temperature for at least one hour before removing the treats from the bag.