In a large microwave-safe bowl, melt the butter and mini marshmallows in two 30-second intervals, stirring between each interval until fully melted and smooth.

Be careful not to overheat — you just want everything melted and combined.

Once the butter and marshmallows are fully melted and smooth, stir in the vanilla extract until incorporated.

Add the Rice Krispies cereal to the marshmallow mixture.

Gently fold and mix until the cereal is evenly coated.

Fold in the Lucky Charms marshmallows, mixing just until evenly distributed throughout the mixture.

Transfer the mixture into a parchment-lined 8×8-inch square pan.

Use a spatula (or lightly greased hands) to gently press the mixture down evenly. Do not press too hard — this keeps the bars soft and chewy.

Sprinkle extra Lucky Charms marshmallows on top and lightly press them into the surface.

Let the bars chill for 60–90 minutes, or until fully set.

Cut into 9 squares (3×3).

Enjoy fresh, or store in an airtight container for up to 8 days.