Gather all ingredients for the main recipe and your chosen flavor variations. Line a 9x13 inch baking pan with parchment paper or grease it well.

In a large microwave-safe bowl, combine the butter and mini marshmallows. Microwave on high for 1 minute, then stir, and continue microwaving in 30-second intervals until melted and smooth.

Add the Rice Krispies cereal to the melted marshmallow mixture and stir until evenly coated. Divide the mixture into three equal portions in separate bowls.

For the classic flavor, stir in vanilla extract into one portion. For the chocolate flavor, mix in cocoa powder and chocolate chips into the second portion. For the fruity flavor, incorporate crushed freeze-dried berries and lemon zest into the third portion.

Press each flavored mixture evenly into the prepared baking pan, keeping them separate to form three distinct sections. Let the treats cool completely on the counter or in the refrigerator before cutting and serving.