In a large saucepan over medium-high heat, melt butter, stirring constantly, until just browned. Stir in mini marshmallows, peanut butter and salt until smooth and glossy. Remove from heat.

Using a spatula or wooden spoon, stir in crispy rice cereal until well coated. Transfer mixture to a greased 8-by-8-inch square pan; using spatula or lightly greased fingers, press down firmly and evenly into bottom and sides of pan.

Let mixture set for at least 30 minutes before cutting into 9 square bars. Bars will stay fresh, individually wrapped in plastic wrap, at room temperature for up to 4 days.