
Lightly grease a 9x13 inch pan with butter or non-stick cooking spray.
In a large saucepan melt the butter, mini marshmallows and peanut butter together over low heat while stirring gently.
Once melted, remove from the heat and stir in the Rice Krispies.
Press the mixture into the pan (lightly spray your hands with non-stick cooking spray to avoid the mixture sticking to your hands).
Add the chocolate chips to a medium-sized heatproof bowl and microwave for 45-second intervals, stirring in between each burst until smooth.
Stir in the vegetable oil and pour the chocolate over the top of the bars.
Let harden at room temperature for about 2 hours, cut into squares and store in an airtight container.