Preheat the oven to 350°F, and line a 9x9 baking pan with parchment paper. Then, lightly grease the parchment paper, and set aside.
In a small saucepan, combine the butter and chocolate chips. Stir on low heat until fully melted and smooth. Once smooth, set aside to cool slightly.
½ cup unsalted butter, ¾ cup milk chocolate chips, ¾ cup dark chocolate chips
While the chocolate mixture cools, combine the eggs and sugar. Using an electric hand mixer (or a stand mixer), beat the eggs, granulated sugar, and brown sugar until fully incorporated.
3 large eggs, 1 cup granulated sugar, ½ cup light brown sugar
Pour in the sourdough starter and beat until fully incorporated. Now add in the chocolate mixture and mix until smooth.
½ cup sourdough starter
In a small mixing bowl, combine the flour, cocoa powder, and sea salt.
1 cup all-purpose flour, ½ cup cocoa powder, 1 teaspoon maldon sea salt
Add the dry ingredients to the wet ingredients and beat until just combined, making sure to not overmix.
Pour the batter into the prepared baking pan, then sprinkle with flaky sea salt. Bake for 25-35 minutes until the edges are slightly crispy and the middle is slightly gooey.
Allow the brownies to cool, cut and serve! Enjoy with a glass of milk or even with a scoop of vanilla ice cream!
See post for storage options.