1. Line a 9×13-inch baking dish with parchment paper or grease lightly.

2. Melt butter in a large saucepan over low heat.

3. Add mini marshmallows and stir until fully melted and smooth.

4. Remove pan from heat and stir in vanilla extract.

5. Fold Rice Krispies cereal into the marshmallow mixture until evenly coated.

6. Let mixture cool 1 minute to prevent candy corn from melting.

7. Gently fold in candy corn pieces to distribute evenly.

8. Transfer mixture to prepared pan and press down gently with a buttered spatula or wax paper.

9. Melt white chocolate chips with vegetable oil in 20-second microwave bursts, stirring until smooth.

10. Drizzle melted white chocolate over the top and add sprinkles if desired.

11. Let bars cool at room temperature about 30 minutes until set.

12. Cut into squares or rectangles and serve.