Melt butter in a large pot over medium-low heat
Add rosemary and thyme sprigs and stir consistently until butter foams and milk solids brown, about 4-5 minutes (do not let it burn)
Remove the herb sprigs from the browned butter
Add marshmallows and stir until completely melted
Turn off heat and add rice krispies cereal, corn flakes cereal, and chopped pecans
Stir until all ingredients are evenly distributed
Transfer mixture to a lightly greased 9x9 baking dish
Press into an even layer
Garnish with thyme leaves and flaky sea salt
Slice into squares and serve
