Line a 8- or 9-inch square pan with parchment paper and spray with cooking spray.
Heat butter and pecans over medium heat in a large saucepan or stock pot.
Stir often and heat until the butter foams. The foam will subside, keep stirring until the butter and pecans are browned, fragrant, and toasted.
Remove the pot from the heat. Stir in marshmallows and the milk until everything is melted together.
Stir in the rice cereal until well mixed.
Transfer the mixture to the prepared pan and press down with greased fingers until the mixture is in a flat layer.
Cool the bars for at least 30 minutes at room temperature. Remove the batch from the pan using the parchment paper and slice into 16 squares using a sharp knife over a cutting board.
Nutrition facts are sometimes provided below and are calculated using an online calculator. With specific brands of ingredients and additions, omissions, or substitutions the nutrition facts may change. We encourage you to use your own nutrition facts caculator to obtain the most accurate nutrition facts for your meal.