Prepare the Pan: Start by spraying a 9x9-inch baking pan with non-stick spray. Line it with parchment or foil, allowing some overhang for easy removal later.

Brown the Butter: In a large pot, melt the unsalted butter over medium heat. Continue cooking until the butter turns a golden brown, stirring frequently—look for brown flecks forming at the bottom.

Melt the Marshmallows: Once the butter is browned, take the pot off the heat. Stir in the mini marshmallows and sea salt, mixing until everything is melted and smooth.

Add Vanilla: Gently stir in the vanilla extract, letting its warm aroma elevate the flavor of your mixture.

Combine with Cereal: In a large bowl, pour the melted marshmallow mixture over the Rice Krispies cereal. Stir well until fully combined and each piece is coated.

Layer the Mixture: Transfer half of the marshmallow mixture into the prepared pan. Press it down evenly, then spread a layer of dulce de leche over the top.

Add Remaining Mixture: Pour the rest of the Rice Krispies mixture over the dulce de leche layer. Press down gently to compact everything together.

Set and Cool: Allow your treats to cool at room temperature until they are completely set, which should take about 30 minutes.