the butter lab's brown butter rhubarb blondies


This recipe is largely adapted from Lisa Ludwinski’s Sister Pie. She calls them “anti-blondies” because, in a genius move, she uses tart rhubarb to cut the sweetness of traditional blondies. Surrounded by gooey blondie-ness, the rhubarb itself becomes more tart and zingy. The contrast between sour and sweet is bold, unexpected, and completely delicious.

The base blondie recipe is similar to others. (I did a side-by-side ingredient comparison between it and Cook’s Illustrated’s, Smitten Kitchen’s, and Mindy Segal’s.) This one has a touch more flour and butter. There’s also no baking powder or baking soda, making it more brownie-like instead of cake-like, which blondie purists tend to prefer. I ended up trying this particular recipe with and without leavening, and was happier leaving it out, as written in the original.

My major changes were to double the salt and nearly triple the vanilla. I also browned the butter, which always makes blondies better. The original recipe calls for sliced almonds and white chocolate, but I used toasted macadamia nuts and the fruity, naturally pink, ruby chocolate that I was way too excited to find at Whole Foods this week. I also broiled the sugar-sugar sprinkled on top. The result was truly an anti-blondie: punchy rhubarb in a gooey bed of brown butter, vanilla and salt, with crunchy macadamia nuts and pockets of melted pink chocolate, all crowned with a crackly, caramelized sugar crust.

The Butter lab’s Brown Butter Rhubarb Blondies

Largely adapted from the rhubarb blondies recipe in Sister Pie by Lisa Ludwinski.

See my changes above. I also included weight measurements where helpful. Use field rhubarb, if you can find some, or thin, firm, colorful stalks, without wrinkles. I really like the combination of macadamia nuts and ruby chocolate here, but substitutes work; find suggestions in the ingredient list. If you don’t have sea salt, just double up on the kosher salt.

Makes 9 bars.

1 cup rhubarb (about 2-3 stalks), cut in 1/2-inch slices
2 teaspoons granulated sugar
1/2 cup plus 2 tablespoons (1 1/4 sticks or 141.5 grams) unsalted butter
1/2 cup (99 grams) light brown sugar
1/2 cup (99 grams) dark brown sugar
2 large eggs, at room temperature
1 tablespoon vanilla bean paste or pure vanilla extract
1 1/4 cups (177.5 grams) all-purpose flour
1 teaspoon kosher salt
1 teaspoon flaky sea salt
1/2 cup macadamia nuts (or almonds or pecans or walnuts)
1/2 cup ruby chocolate (or white chocolate or butterscotch chocolate), roughly chopped
1 1/2 tablespoons granulated sugar
1 1/2 tablespoons turbinado sugar


  • Preheat oven to 350°F. Line a greased 8-inch square baking pan with parchment paper, leaving a 1- to 2-inch overhang. Spread nuts evenly on a sheet pan and toast for 6-10 minutes, shaking the pan halfway through, until fragrant. Cool before roughly chopping.

  • In a small bowl, mix the rhubarb with the granulated sugar and set aside.

  • Brown the butter: Melt butter in a small saucepan over medium heat. Cook, stirring the pan every few seconds, until it turns a deep gold color and starts to smell fragrant, 3-5 minutes. Pour the browned butter into a large mixing bowl.

  • Add the light and dark brown sugars to the browned butter and whisk until smooth. Allow the butter mixture to cool (it should be warm, not hot). Add the eggs and vanilla and fold until smooth.

  • Add the flour and salt and stir until the flour is almost completely incorporated. Add the rhubarb-sugar mixture (leaving behind any sugary water) and the chopped nuts and chocolate. Mix until just combined.

  • Scrape the batter into prepared pan and smooth the surface. Mix 1 1/2 tablespoons granulated sugar with 1 1/2 tablespoons turbinado sugar and sprinkle evenly over the top.

  • Bake for 25 to 30 minutes, until just set. Broil for an extra minute or two to caramelize the sugar, watching the oven closely so that the blondies don’t burn!

  • Remove the pan from the oven and cool completely on a wire rack. Use the parchment overhang to lift the blondies out of the pan and onto a cutting board. Use a sharp knife to cut into 9 bars. Store in an airtight container at room temperature for up to 4 days.

May 30, 2019