Preheat oven to 300 degrees.

Prepare baking dish: spray and 8 by 8-inch baking dish with non-stick cooking spray, set aside.

Melt butter: place butter in a large microwave safe bowl. Heat in microwave until just melted.

Mix in sweetener and salt: Stir in sugar and salt, let cool slightly if warm.

Mix in wet ingredients: add in eggs and vanilla. Break yolks and stir with wooden spoon just until blended.

Mix in dry ingredients: add in flour, cocoa powder and chocolate chips. Fold and stir mixture with wooden spoon just until combined.

Add batter to pan: pour into prepared baking dish. Spread into an even layer. Bake in preheated oven just until barely set, about 40 – 46 minutes (toothpick may have a bit of sticky batter, careful not to over-bake).

Cool before cutting (if you can wait!): let cool completely on a wire rack then cut into individual squares. Store in an airtight container at room temperature.