1. Line a 9×13 inch baking pan with parchment paper, leaving overhang. Grease paper lightly.

2. In a large microwave-safe bowl, melt butter and marshmallows in microwave: heat 1 minute, stir, then 30-second intervals until smooth. Alternatively, melt on stovetop over low heat.

3. In a separate bowl, mash bananas. Stir in dry pudding mix, milk, and vanilla extract until well combined.

4. Pour banana mixture into melted marshmallow mixture and stir until fully blended.

5. Add Rice Krispies cereal and fold gently until evenly coated.

6. Transfer mixture to prepared pan. Using a greased spatula or wax paper, press evenly and firmly into a compact layer. Do not overpress.

7. If desired, sprinkle crushed Nilla wafers on top and press gently. Garnish with fresh banana slices (tossed with lemon juice to prevent browning).

8. Refrigerate for at least 2 hours until set.

9. Lift treats from pan using parchment overhang, cut into squares with a greased knife, and serve.