Rhubarb And White Chocolate Blondies Recipe

Rhubarb is one of the most unique vegetables, with its tangy celery-like stalks, crimson hues, and complex flavor that is a mash-up of apple, citrus, and grape. Most people equate rhubarb with pie or other sweet desserts, but the veggie was first used thousands of years ago in China, Greece, and Rome for medicinal purposes. For many today, rhubarb is a harbinger of spring, and it adds its rosy twang to any recipe it's used in.

These rhubarb and white chocolate blondies  –  courtesy of recipe developer Julie Kinnaird  –  combine butterscotchy bars with swirls of tangy rhubarb compote flavored with vanilla and sweetened with brown sugar. This recipe is simple to prepare but loaded with complex flavors. The blondies are made extra rich because we brown the butter, which adds a deep and nutty flavor to the batter. Brown sugar gives a hint of caramel, and smooth white chocolate balances the tangy compote. The fresh rhubarb cooks down quickly and takes on the deep vanilla bean flavor. Blondies are often considered to be overly sweet, but in this recipe, the tart rhubarb is key in creating a perfect harmony of flavors. This blondie recipe can be made in advance and the recipe doubles well, so you can freeze half and take the rest to your next picnic.

For this recipe, you will need two large stalks of fresh rhubarb. Rhubarb grows in a range of colors from green to crimson but using a deep red variety in this recipe will give the most visual appeal. The rhubarb is cooked down with light brown sugar, water, and a vanilla bean for intense flavor. The rhubarb compote is swirled into blondie batter made from unsalted butter (which is transformed into a rich and nutty brown butter), brown sugar, an egg, vanilla extract, all-purpose flour, sea salt, and chopped white chocolate. 

Split the vanilla bean lengthwise to expose the seeds.

Cut the rhubarb into ½-inch slices (you should have about 2 cups).

Add the vanilla bean, rhubarb, ⅓ cup brown sugar, and water to a large heavy saucepan.

Bring to a simmer over medium heat and cook, stirring frequently, until the rhubarb is very soft and the mixture has thickened.

Transfer the rhubarb compote to a heat-proof bowl and chill until ready to use.

Preheat the oven to 350 F.

Melt the butter over medium heat in a small saucepan or saute pan.

Once the butter starts to foam, reduce the heat slightly and cook and stir for about 5 minutes until it reaches a deep golden brown color.

Transfer the butter to a large heat-proof bowl and cool slightly.

Grease and line an 8-inch square baking pan with parchment, leaving a 1-inch overhang on 2 sides.

Add the remaining 1 cup brown sugar to the butter and stir until smooth.

Add the egg and vanilla extract and beat until fully incorporated.

Carefully stir in the flour and salt. Continue to mix until well combined and smooth.

Stir in the white chocolate.

Transfer the blondie batter to the prepared pan and smooth the top.

Remove the vanilla bean from the rhubarb compote and use a small knife to scrape out the seeds.

Stir the seeds into the compote.

Place spoonfuls of the rhubarb evenly on top of the blondie batter.

Use the tip of a knife to swirl the rhubarb into the blondies.

Bake the blondies for 25-30 minutes until golden brown.

Cool the blondies completely on a rack, then use the parchment overhang to lift them out of the pan.

Cut the blondies into 16 small squares and serve.

If you have access to fresh-grown rhubarb, Kinnaird says that the best way to harvest stalks is by twisting them from the base of the plant when picking, rather than cutting them off. This makes it easier for the plant to regenerate. Find stalks that are 8-10 inches long and at least an inch in width. Older, larger stalks of rhubarb can be tough and dry on the inside. If you are purchasing rhubarb at the market, avoid stalks that have blemishes or bruises and make sure that they are firm and crisp. 

Because rhubarb has such an astringent tart flavor, it is best cooked with sweeteners. Strawberries and rhubarb are a classic combination for pies, tarts, cakes, and sauces but rhubarb also pairs beautifully with apples, plums, and other berries. Rhubarb tends to become mushy when baked so make sure to have adequate starch to absorb the juices. Kinnaird suggests tossing chopped rhubarb with cornstarch or flour before adding it to baked goods to help absorb moisture. She also loves pickling rhubarb in a brine for a tasty addition to burgers, sandwiches, or a charcuterie board. Rhubarb can also be sliced and frozen to use all year round. Simply add it to recipes before thawing as you would use fresh. Rhubarb is loaded with antioxidants, fiber, potassium, calcium, and vitamins C and K, so it is a great ingredient to incorporate into sweet and savory preparations.

White chocolate is a confection made from cocoa butter, milk solids, sugar, and usually a bit of vanilla. The way white chocolate is labeled can be confusing, which makes it difficult to decide on the best kind to purchase for baking purposes. In order to be legally called white chocolate, the confection must contain at least 20% cocoa butter and 3.5% milk solids. 

Products labeled as "white baking chips" or "white baking bars" are typically made from milk, sugar, and oils, with very little cocoa butter if any at all. For this recipe, Kinnaird prefers to use high-quality white chocolate containing at least 30% cocoa butter. The reason for this is that the higher the cocoa butter percentage, the more smoothly the white chocolate melts during baking. White baking chips also have a higher percentage of sugar, which might make the blondies a bit cloying despite the tartness of the rhubarb.