Begin by greasing a 9x9 inch baking pan with butter or non-stick spray to ensure easy removal.

In a large pot over medium heat, combine 4 tablespoons of butter with 4 cups of mini marshmallows. Stir until smooth and melted.

Remove from heat and gently fold in 1 tablespoon of freshly grated lemon zest.

Pour in 6 cups of Rice Krispies cereal and fold gently until well-coated.

Transfer to the greased baking pan and press down evenly with a spatula.

Melt 1/2 cup of white chocolate in a microwave-safe bowl and drizzle over the treats.

Allow to cool at room temperature for about 30 minutes, then cut into squares.