In a large pot (I use a 3 qt. Dutch oven), begin to melt the butter over medium heat. Once the butter is almost completely melted, add the honey and peanut butter. Whisk the ingredients together. The ingredients should bubble and foam. Keep an eye on the bubbling, and continue to cook the ingredients for about 3 minutes, stirring often.Remove the pot from the heat, and add the vanilla extract. The ingredients will bubble slightly with the addition of the alcohol from the vanilla. This is normal.Stir in the puffed rice cereal.Pour the cereal mixture into a parchment-lined 8x8 baking pan. I like to leave a bit of extra parchment overflowing on the sides of the pan so I can easily remove the rice treats after refrigeration. Press the rice treats down into the pan. The top of the treats should appear smooth versus lumpy.Refrigerate the rice treats for about 1-2 hours. Alternatively, you can place the rice treats in the freezer for about 30 minutes. You'll know the rice treats are ready to cut when they feel firm on top.Remove the parchment (and rice treats) from the pan. Cut the rice treats into squares.Keep the bars refrigerated in an air-tight container.