Preheat oven to 340°F. Line a 9 x 13-inch baking pan with parchment paper.
In a saucepan, combine butter, honey, and brown sugar. Cook over low heat, stirring until melted and combined. Bring just to a bubble, then remove from heat.
Stir in coconut, oats, and cornflakes until evenly coated.
Press mixture evenly into prepared pan.
Bake for 12–15 minutes, until golden and crispy around the edges.
Cool completely in the pan before cutting into bars.
Store in an airtight container at room temperature for up to 5 days.
