Line a 9x13-inch pan with parchment; grease lightly with the extra butter.
Warm butter in a large pot over medium-low heat.
Stir in marshmallows; cook, stirring, until fully melted and smooth.
Remove from heat. Mix in vanilla and a small pinch of salt.
Add cereal and fold until every piece is coated.
Press mixture into the pan with a buttered spatula, gently.
Let cool until set, then cut into squares.
Notes
Try a swirl of 2 tbsp creamy peanut butter with the melted marshmallows, or drizzle the cooled bars with melted white chocolate. For a hint of warmth, add a pinch of cinnamon. Store in an airtight container at room temperature for up to 3 days; briefly microwave a bar for 5–8 seconds to soften.This recipe is an original creation inspired by classic Crispy Golden Cheerios Treats flavors. All ingredient ratios and instructions are independently developed.