Preheat oven to 325°. Fill an 8x8-inch pan with 1 inch hot water, and place in oven. Spray a 6-inch round cake pan with baking spray, and line bottom with parchment paper; set aside.
In a small microwave-safe bowl, melt chocolate and butter on High (100 percent power) for 30-second intervals, stirring after each, until melted and smooth (approximately 11/2 minutes total). Let chocolate mixture cool slightly.
In a medium bowl, whisk together egg yolks and vanilla extract until well combined. Whisk in chocolate mixture until smooth.
In a separate bowl, combine sugar, cocoa, and salt. Stir sugar mixture into chocolate mixture until well combined.
In a separate bowl, beat egg whites with a mixer at medium speed until soft peaks form. Fold egg whites into chocolate mixture in thirds. Spoon batter into prepared pan. Place in oven in center of 8x8-inch pan. Bake for 50 to 55 minutes, or until a wooden toothpick inserted in center comes out clean.
Remove cake from water bath; let cool in pan on wire rack for 10 minutes. Remove from pan, and let cool completely.
To serve, warm hot fudge topping according to package directions; spoon over top of cake. Garnish with whipped cream, chocolate curls, and fresh strawberries, if desired.
Recipe by Southern Lady Magazine at https://southernladymagazine.com/flourless-chocolate-cake-recipe/