Preheat oven to 350℉. Line an 8x8 baking pan with parchment paper and set aside.
In a large microwave-safe bowl, heat butter and finely chopped chocolate for 30 seconds. Mix and then heat in 10-second intervals (mixing in between) until the mixture is smooth and melted together. Once melted, add the sugar and whisk until combined.
10 tablespoon unsalted butter, 4 oz semisweet chocolate, finely chopped, 1 cup granulated sugar
Add the eggs, egg yolk, and vanilla and whisk vigorously for about 1-2 minutes until you see little bubbles form on top.
2 large eggs, 1 large egg yolk, 1½ teaspoon vanilla extract
Add the flour, cocoa powder, and salt and mix until everything is just combined, then use a rubber spatula to fold in the chocolate chips.
½ cup all-purpose flour, ¼ cup dutch-processed cocoa powder, 1 teaspoon salt, ½ cup semi-sweet chocolate chips
Pour into the parchment paper-lined pan and bake for 30-35 minutes, until the center of your brownies are set or a toothpick/knife comes out of the center with moist crumbs. Let cool for about 30 minutes and then cut.
Optional: add toppings like melted chocolate and flaky sea salt! Serve with your favorite flavor of ice cream.