Brown Butter Marshmallow Bar Recipe

Prepare pan

Preheat oven to 350°F (175°C). Line a 9x9-inch baking pan with parchment paper, leaving an overhang on two opposite sides to lift out the bars. Lightly grease the parchment.

Brown butter

In a small saucepan over medium heat, melt 1 cup unsalted butter. Continue cooking, swirling the pan occasionally, until the butter foams, the milk solids turn golden-brown and a nutty aroma develops, about 6–8 minutes. Immediately remove from heat and pour into a heatproof bowl to stop cooking. Let cool until warm but pourable, about 10 minutes.

Make dough

In a medium bowl whisk together 1 3/4 cups all-purpose flour, 1/2 cup granulated sugar and 1/4 tsp fine sea salt. Stir in 1 tsp vanilla. Pour the warm browned butter into the dry ingredients and mix with a spatula until a cohesive dough forms (it will be crumbly but hold together when pressed).

Bake crust

Press the dough evenly into the prepared 9x9 pan, compacting firmly to create an even layer. Bake in the preheated oven for 18–22 minutes, until edges are lightly golden. Remove from oven and allow to cool to room temperature in the pan on a wire rack (do not remove from pan).

Bloom gelatin

Place 1/4 cup cold water in a small heatproof bowl and sprinkle 2 1/2 tsp unflavored gelatin evenly over the surface. Let sit to bloom while you make the sugar syrup, about 5–10 minutes.

Cook sugar syrup

Combine 1 cup granulated sugar, 1/4 cup corn syrup, and 1/4 cup cold water in a small saucepan. Stir over medium heat just until sugar dissolves, then clip a candy thermometer to the pan and bring to a boil without stirring. Cook until the syrup reaches 240°F (115°C), soft-ball stage, about 6–8 minutes. Remove from heat.

Whip egg whites

While syrup cooks, place 3 room-temperature egg whites and 1/8 tsp fine sea salt in the bowl of a stand mixer fitted with the whisk attachment (or a large bowl with a hand mixer). Whip on medium-high speed to soft peaks.

Combine syrup and gelatin

When syrup reaches 240°F, carefully pour the hot syrup in a thin, steady stream into the whipped egg whites while the mixer runs on low-to-medium speed. After all syrup is added, immediately add the bloomed gelatin (microwave the gelatin briefly—5–8 seconds—if it hasn’t fully melted) and continue whipping on high until the mixture is glossy, thick and triples in volume, about 5–7 minutes. Add 1 tsp vanilla and whip 10–15 more seconds to combine.

Spread marshmallow

Working quickly while the marshmallow is still warm and spreadable, use an offset spatula or lightly oiled spatula to spread the marshmallow evenly over the cooled shortbread in the pan to a 1/2–3/4-inch thickness. Smooth the top as best you can. Let the marshmallow set at room temperature for about 1 hour (or place in a cool spot) until it is no longer tacky to the touch.

Brown butter for topping

In a small skillet, melt 2 tbsp unsalted butter over medium heat and cook until the milk solids brown and the butter smells nutty, about 3–4 minutes. Remove from heat and let cool slightly.

Top and salt

Once the marshmallow is set, drizzle the warm browned butter evenly over the marshmallow surface (a little goes a long way). Immediately sprinkle 1/2 tsp coarse sea salt evenly over the top.

Finish and cut

Dust a large cutting board or the top of the marshmallow lightly with 1 tbsp confectioners' sugar to prevent sticking. Using the parchment overhang, lift the slab from the pan. Using a sharp knife dipped in hot water and wiped dry between cuts (or a bench scraper), cut into 16 bars (4x4) or 9 larger bars (3x3). Wipe the knife and reheat as needed to get clean cuts. Store in an airtight container at room temperature separated by parchment for up to 3 days, or refrigerate for up to 5 days (bring to room temp before serving).