Sourdough Blondie Brownie Swirl Bars (Brondies)
These sourdough Brondie bars start with one shared wet base split into two bowls: one becomes a chewy white chocolate blondie and the other becomes a fudgy semi sweet brownie. Swirled together and baked in one pan, every bar gives you both in every single bite.
Servings: 16 bars
Calories: 290kcal
Equipment
- 9x9 inch square baking pan
- Parchment paper
- 2 large mixing bowls
- Whisk
- spatula
- kitchen scale
Ingredients
Wet Base
- 169 g melted butter 3/4 cup
- 150 g light brown sugar 3/4 cup packed
- 100 g granulated white sugar 1/2 cup
- 10 g honey 2 teaspoons
- 2 large eggs room temperature
- 150 g sourdough starter active or discard 100% hydration 2/3 cup
- 6 g vanilla extract 1.5 teaspoons
Blondie Half
- 145 g all purpose flour 1 cup + 2 tablespoons
- 2 g baking soda 1/2 teaspoon
- 1 g baking powder 1/4 teaspoon
- 3 g salt 1/2 teaspoon
- 85 g mini white chocolate chips just over 1/2 cup
Brownie Half
- 110 g all purpose flour 3/4 cup + 2 tablespoons
- 30 g natural unsweetened cocoa powder 1/4 cup + 1 tablespoon
- 2 g baking soda 1/2 teaspoon
- 1 g baking powder 1/4 teaspoon
- 3 g salt 1/2 teaspoon
- 85 g mini semi sweet chocolate chips just over 1/2 cup
Instructions
- Preheat oven to 350 degrees F. Line a 9x9 inch pan with parchment paper leaving an overhang on two opposite sides.
- Get two bowls for the separate Blondie and Brownie dry ingredients.
- To the first bowl add 145g flour, 2g baking soda, 1g baking powder, and 3g salt. Stir until just combined then fold in 85g mini white chocolate chips. This is for your blondie batter.
- To the second bowl add 110g flour, 30g cocoa powder, 2g baking soda, 1g baking powder, and 3g salt. Stir until just combined then fold in 85g mini semi sweet chocolate chips. This is for your brownie batter.
- In a large bowl whisk together melted butter, brown sugar, white sugar, honey, eggs, sourdough starter, and vanilla until smooth and fully combined with no streaks.
- Divide the wet mixture evenly between two bowls. Each bowl should have approximately 342g.
- Drop alternating spoonfuls of blondie and brownie batter across the prepared pan until both bowls are empty. See notes for swirl options and long fermentation options.
- Bake at 350 degrees F for 25 to 30 minutes. Edges should be set and pulling slightly from the pan. Center should have a very slight wobble. A toothpick inserted in the center should come out with moist crumbs not wet batter. Do not overbake.
- Cool completely in the pan for at least 2 hours before cutting. For cleanest cuts refrigerate the fully cooled slab for 1 hour then slice into a 4x4 grid for 16 bars.
Notes
The Swirl: Three Options
Option one: skip the swirl entirely. Drop alternating blobs of batter into the pan and bake as is. The two batters bake up with distinct pockets of blondie and brownie throughout. This is the easiest method and looks beautiful.
Option two: swirl before baking. Using a butter knife or skewer drag through the batter in three to four lazy S curves. Stop earlier than you think you need to. Overworking the swirl muddies the two batters together and loses the contrast.
Option three: the five minute oven swirl. Place the assembled pan in the oven for five minutes first. Pull it out and swirl quickly while the top is shiny and soft. The brief heat melts the butter back down and makes swirling significantly easier with cleaner ribbon results. Get it back in the oven before the edges begin to set.
Chocolate Chip Size
Mini chips are recommended for even distribution throughout both halves. If substituting use these gram amounts per half: regular chips 80g, chunks 70g. This applies to both the white chocolate in the blondie half and the semi sweet or dark chocolate in the brownie half.
Baking and Doneness
These bars are meant to look slightly underdone when you pull them from the oven. They continue to set during cooling. Pulling at the 25 to 30 minute mark with a slight center wobble is correct. Do not push past 30 minutes or the bars will be dry. The toothpick test is your most reliable doneness cue here, not a thermometer.
Fridge Ferment Option
Mix the full batter, split between two bowls, add dry ingredients and mix ins to each half, then cover and refrigerate overnight. In the morning either scoop cold directly into the pan and add two to three extra minutes of bake time, or bring to room temperature for one hour before baking. Cold batter holds its shape better for the blob method. Room temperature batter is easier to swirl.
No Sourdough Starter
Replace the 150g of starter with 75g all purpose flour and 75g whole milk whisked together until smooth. The milk adds fat and richness that water alone cannot replicate. The flavor will be slightly simpler but the texture will hold up well.
Storage
Store in an airtight container at room temperature for up to 5 days or refrigerate for up to 1 week. Freeze individually wrapped bars for up to 3 months. Thaw at room temperature for one hour or warm in a 300 degree F oven for five minutes straight from frozen.
