Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

Melt the salted butter in a saucepan over medium heat until golden brown and nutty, about 5–7 minutes, then cool slightly.

In a mixing bowl, combine the cooled browned butter with both sugars and mix until creamy. Add the egg and vanilla extract, blending together.

In a separate bowl, whisk together baking soda, salt, and flour. Gradually mix into the wet ingredients, being careful not to overmix.

Fold in the Rice Krispies and mini marshmallows until evenly distributed.

Scoop large mounds of dough (about 3 tablespoons each) onto the prepared baking sheet, ensuring space in between.

Bake for 10–13 minutes until the edges are light golden brown and centers remain soft.

Cool on the baking sheet for 5 minutes before transferring to a wire rack. Sprinkle with flaked salt before serving.