Generously butter a 9x13 inch baking dish. Set aside.
In a large pot, melt the butter over low heat. If the heat is up too high, your marshmallow treats may end up hard. Melt it low and slow together.
Add the mini marshmallows and heat, stirring often until melted and smooth.
Remove from heat and stir in vanilla extract. Mix well and gently stir in the cereal.
Using a piece of parchment paper or a buttered rubber spatula, gently press the treats into prepared pan. Allow to set for 30 minutes before cutting into squares.
Store at room temperature in an airtight container and eat within 3 days for the best flavor and texture.
Notes
The calories shown are based on the recipe making 12 bars, with 1 serving being 1 cereal bar. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information.**