Preheat the oven to 350°F and grease an 8x8 inch pan then line with parchment paper.
Melt the butter and chocolate together in a double boiler over low heat, taking care not to overheat by mixing throughout the process. Once melted, remove from heat and allow the mixture to cool until the temperature is lukewarm.
5 ounces Semisweet chocolate , 6 tablespoons Unsalted butter
Whisk together the egg, egg yolks, oil, greek yogurt, and vanilla extract in a medium bowl. Mix in the chocolate and butter combination then add sugars and whisk to combine.
1 Egg, 2 Egg yolks, ½ cup Neutral oil, ¼ cup Greek yogurt, 1 teaspoons Vanilla extract, ½ cup Granulated sugar, ½ cup Brown Sugar
Sift the all-purpose flour and black cocoa powder into the bowl with wet ingredients and add kosher salt. Fold everything together until the flour has been incorporated before adding chocolate and folding once more with a spatula.
1 cup All-purpose flour, ¼ cup Black cocoa powder, 1 teaspoon Kosher salt, 1 cup Milk chocolate
Bake the brownies for 23-25 minutes - you should see that the tops of the brownies are no longer wet, but still quite soft when you gently press on them. If you’re feeling scientific, shoot for an internal temp of 180-190F with an instant read thermometer.
Remove from the oven and let them cool for about 20 minutes before cutting into squares and enjoying. If you prefer extra sharp edges, allow the brownies to cool further in the fridge for about an hour before cutting!