Lightly grease a 9 x 13 baking dish or line with parchment paper, leaving some overhang to lift out the treats later.
In a large saucepan, over low to medium heat, melt the butter just until it's bubbly and golden.
3 Tablespoons butter
Next, stir in the marshmallows and vanilla extract. Stir for a minute or so, until the marshmallows are completely melted and smooth. If you're using regular-size marshmallows, give them a little extra time.
10 ounces mini marshmallows, ½ teaspoon vanilla extract
Now mix in the creamy peanut butter until everything is silky and combined.
½ cup creamy peanut butter
Take the pan off the heat and stir in the rice krispies. Gently fold in the cereal until every piece is coated. Work fast, the mixture sets quickly.
6 cups Rice Krispies cereal
Transfer the mixture to a greased (or parchment lined) 9 x 13 pan. Use a spatula or a piece of wax paper to press everything down evenly.
Let set at room temperature for a few minutes (don't worry, it doesn't take long). Then cut into squares and enjoy!