The recipe is from America's Test Kitchen:
8 Tablespoons unsalted butter
3 oz. unsweetened chocolate (make sure its unsweetened)
1 cup sugar
2 large eggs
1 teaspoon vanilla extract
1/2 teaspoon baking powder
1/4 teaspoon salt
2/3 cup all-purpose flour
Heat oven to 350
Melt butter and chocolate together in microwave, 1 -3 minutes. Let mixture cool slightly
Whisk the sugar, eggs, vanilla extract, baking powder and salt in a large bowl until combined.
Whisk in melted chocolate mixture until smooth.
Stir in the flour until no streaks remain.
Scrape batter into 8x8 pan, sprayed lightly with vegetable oil
Bake 22-27 minutes until inserted toothpick comes out clean.
Easy Peasy! And sooooo yummy!