Lightly grease a 9×13-inch baking pan with butter or nonstick cooking spray. You can also line it with parchment paper for easier removal.

1. Melt the butter.In a large saucepan, melt the butter over low heat.
2. Add the marshmallows.Stir in the mini marshmallows until completely melted and smooth. Keep the heat low to prevent the mixture from becoming too hot and making the treats hard.
3. Add the lemon flavor.Remove the saucepan from the heat. Stir in the lemon juice, lemon zest, vanilla extract, salt, and optional yellow food coloring until evenly combined.
4. Mix in the cereal.Add the crispy rice cereal and gently fold until every piece is coated with the marshmallow mixture.
5. Press into the pan.Transfer the mixture to the prepared pan. Using a lightly buttered spatula or greased hands, gently press it into an even layer. Avoid packing it too tightly so the treats stay soft and chewy.
6. Prepare the glaze (optional).Whisk the powdered sugar with enough lemon juice to create a smooth, pourable glaze.
7. Cool and finish.Let the treats cool at room temperature for about 30–45 minutes. Drizzle with the lemon glaze, if desired, and sprinkle with extra lemon zest.
8. Slice and serve.Once set, cut into squares and enjoy your homemade lemon treats.