Preheat oven to 350 Fahrenheit. Use two 16 inch long sheets of parchment paper or aluminum foil to line an eight inch square pan by folding both sheets lengthwise to be eight inches wide. Place the first sheet in the bottom of the pan so the ends hang over the sides. Lay the second sheet in the pan perpendicular to the first sheet with the ends hanging over the sides. This will make your brownies easier to lift out of the pan and to cut without crumbling.
Combine chocolate and butter in a small heavy saucepan and heat over low flame, stirring constantly with a wooden spoon. When chocolate and butter are mostly melted and only a few lumps remain, remove from heat and stir in cocoa powder and sugar. Stir until mixture is smooth. Whisk in the eggs, one at a time. Whisk in the yogurt. Add in vanilla, salt, and flour and stir briefly to incorporate. Briefly mix in chocolate chips.
Pour mixture into prepared pan and bake for 20 to 25 minutes, until a toothpick inserted in the middle comes out a little chocolaty. Cool on a rack and remove from pan by lifting opposite ends of the foil from the pan. Make seven cuts on one side and four cuts on the other to make 32 1x2 inch brownies.