In a medium saucepan over medium heat, melt 4 tablespoons of unsalted butter until golden brown, about 5-7 minutes.

Add 24 ounces of mini or standard marshmallows to the browned butter and stir over low heat until fully melted, about 3-4 minutes.

In a large mixing bowl, mix together 4 cups of rice crisp cereal and 2 cups of cornflakes, then drizzle the warm marshmallow mixture over the cereal blend, mixing until coated.

Prepare a 9x13 inch baking pan, then transfer the crispy mixture into the pan, pressing down firmly and evenly.

While warm, sprinkle a pinch of flaky sea salt over the top and let sit for about 10-15 minutes to cool slightly.

Allow to cool completely in the pan for about 30 minutes, then cut into squares or rectangles for serving.