Use butter or vegetable spray to grease a 9" x 18"

Melt butter in large saucepan over medium low heat.

Add marshmallows and stir.

When marshmallows are about half melted, add salt, vanilla and butter flavor stirring to combine and continue stirring until the mixture is smooth.

Remove pan from heat from heat.

Pour the Rice Chex into marshmallow mixture and stir to coat evenly and thoroughly.

When cereal is well coated stir in half the sprinkles and all of the white chocolate chips.

Turn mixture into prepared pan and press gently into pan with back of a large, buttered spoon or clean, buttered hands.

Sprinkle with remaining sprinkles.

Allow bars to cool and set.

Cut into 24 bars.