Preheat the oven to 350°F. Spray an 8 x 8-inch baking pan with nonstick cooking spray and line it with parchment paper.
Place the butter and chocolate in a large microwave safe bowl and microwave in 30 second bursts until melted. Whisk in the sugar until dissolved, then whisk in the eggs and vanilla.
Add the flour, salt and Greek yogurt and stir until there are no more streaks of flour. Fold in the chocolate.
Transfer the batter to the prepared pan and spread evenly. Bake in the preheated oven for 25 to 30 minutes, being careful not to overcook them. Allow to cool completely before cutting and serving.
Notes
Storage: These Greek yogurt brownies should be stored in an airtight container. They will keep well for up to 4 days at room temperature.Freezing: The brownies can be frozen for up to 3 months. Wrap well to protect from freezer burn.Tip: Let the brownies cool fully before cutting into squares.