Preheat oven to 325° Fahrenheit. Spray a 9 x 9” square baking pan with nonstick cooking spray. Line with 2 pieces of parchment paper forming a cross. There should be approximately 1 inch of parchment paper coming out from the pan on all sides.

Whisk flour, cocoa, baking powder and salt in a small bowl.

Melt butter and both chocolates over a double boiler until melted.

In a large bowl, whisk together eggs, sugar and vanilla extract for approximately 1 minute or until the eggs turn slightly lighter in color.

Add melted chocolate and butter mixture to the eggs and whisk well.

Using a rubber spatula, fold in dry ingredients and blend well.

Add yogurt, nuts, chocolate chunks and blend well.

Spread batter evenly into prepared pan.

Bake for approximately 40 minutes or until a small sharp knife inserted into the center comes out almost clean.

In a medium saucepan, heat the heavy cream and corn syrup until the mixture comes to a simmer. Remove from the heat and add the chocolate chips.

Whisk until the mixture is fully melted.

Pour the fudge frosting over the baked brownies and spread evenly with an offset spatula.

Sprinkle flaky sea salt over the frosting, if desired.

Chill in the refrigerator until the brownies and frosting are firm.

Gently pull the brownies out of the pan using the parchment paper to lift them out.

Using a chef’s knife, cut the brownies into 16 small pieces.

Store the brownies in an airtight container in the refrigerator until ready to serve.