I'm all for simplifying desserts by figuring out a way to dirty as few things in the kitchen as possible. This is the opposite of that. This is a simple dessert made complicated and dirties at least five bowls, three spatulas, a candy thermometer, and a baking dish.
But when "it's the best dessert I've ever made" (thank you, Ben), I don't mind making a mess in the kitchen. And trust me, the mess won't be your biggest concern. Stopping yourself from eating the entire pan will be.
Brown Butter Rice Krispie Treats
8 oz unsalted butter
11 cups cereal (8 cups rice krispies, 3 cups kix)
2 envelopes (1/2 ounce) unflavored gelatin powder
1/4 cup cool water
1 tbsp vanilla
1/2 cup water
1 cup light corn syrup
2 1/4 cups sugar
1 tsp salt
Make the rice krispie treats: Melt the butter in a stainless steel pot over medium heat. Continue stirring, scraping the brown bits that form on the bottom of the pot, until the butter is golden and no longer bubbling. Pour into a heat resistant bowl making sure to include all of the brown bits.
Pour the cereal into a roasting pan or dutch oven and place in oven. Set to 175.
In a small bowl, mix gelatin, 1/4 cup water, and vanilla.
Combine the remaining water, corn syrup, sugar, and salt in a 3-quart stainless steel pot. Stir until fully incorporated, about 8 minutes. Clip on a candy thermometer and cook without stirring until the mixture reaches 250 degrees.
Transfer the thermometer to a bowl of a stand mixer and pour the syrup in all at once. Cool to 212 degrees, about 8 minutes, then add the gelatin mixture. With the whisk attachment, mix on low speed to combine, then increase to medium-high and whip until the syrup is bright white and tripled in volume, about 5 minutes. Meanwhile, grease a 9 x 13" pan or line with parchment paper.
When the creme is thick, reduce speed to low, add the brown butter, and return to medium-high for one more minute (the butter will not be fully incorporated). Scrape the mixture over the warmed cereal using a greased spatula. Transfer to the prepared pan and gently press into an even layer. Let stand at room temperature until firm and stop yourself from eating the entire pan.