Generously grease a 9x9-inch pan with softened butter.

In a large mixing bowl, add the crispy rice cereal with the roughly chopped Oreo cookies and stir to combine; set aside.

In a large pot, melt 3 tablespoons butter over medium heat.

Once the butter is melted, stir in the mini marshmallows. Continue to cook, stirring very often, until the marshmallows are completely melted, then immediately remove the pot from the heat.

Quickly pour the melted marshmallows mixture into the bowl of cereal and Oreos. Stir well to coat everything evenly. It is important to work quickly during this step.

Scoop the mixture into the prepared pan and press down to flatten out the top.

Allow the bars to sit at room temperature for 1 hour.

Right at the 1 hour mark, melt the white chocolate.

Then turn the pan over onto a cutting board and shake a bit to release the crispy treats onto the board. Use a large knife to cut into 9 squares if using a 9x9-inch pan, or 12 squares if using a 9x13-inch pan.

Drizzle the melted white chocolate over the bars and allow time for the white chocolate to firm up.

Serve the Oreo Rice Krispy Treats once the chocolate is firm.