Grease a 9x13-inch pan with butter or cooking spray and set aside.

Melt 4 tablespoons of unsalted butter and 10 ounces of mini marshmallows in a large pot over medium heat, stirring until smooth (about 4-5 minutes).

Add the lemon zest and mix well. Fold in 6 cups of Rice Krispies until coated.

Press the mixture into the prepared pan, smoothing the top. Let cool briefly.

Melt 6 ounces of white chocolate and drizzle over the treats once slightly cooled.

Let the treats cool completely (at least 30 minutes), then cut into squares.