Prep the pan: Lightly grease a 9x13-inch baking pan with butter or nonstick spray. For easier removal, line it with parchment and grease the parchment, too.

Melt the butter: In a large pot over low heat, melt the butter gently. Keep the heat low to avoid browning unless you want a toasty flavor.

Add marshmallows: Stir in the mini marshmallows. Keep the heat on low and stir constantly until smooth and fully melted. Take your time here—low and slow prevents scorching and keeps the texture soft.

Flavor it: Remove the pot from the heat. Stir in the vanilla and salt until evenly distributed. This small step makes a big difference in taste.

Add the cereal: Pour in the crispy rice cereal and fold gently with a buttered spatula until every piece is coated. Don’t overmix; stop as soon as it looks even.

Fold in extras (optional): If using chocolate chips or candies, let the mixture cool for 1–2 minutes so they don’t melt completely. Then gently fold them in.

Press into the pan: Transfer the mixture to the prepared pan. Lightly grease your spatula—or your clean hands—and press the mixture into an even layer. Do not pack it down too firmly, or the bars can turn dense and hard.

Set and slice: Let the pan sit at room temperature for 30–45 minutes until set. Slice into squares with a sharp knife. For neat edges, wipe the knife between cuts.

Optional finish: Drizzle with melted chocolate and add a pinch of flaky salt for a sweet-salty finish.