Heat oven to 350℉/177℃.
Spray an 8-inch round pan with baking spray. Set aside.
Place chocolate pieces in a medium bowl.
Microwave in 15 second intervals, stirring after each, until chocolate is completely melted.
Whisk in melted butter and egg yolks. Set aside.
Beat egg whites at high speed of an electric mixer until they start to thicken.
Slowly stream in sugar while continuing to beat.
Add red food coloring.
Continue to beat to stiff peaks.
Fold chocolate mixture into remaining meringue.
Pour into prepared pan.
Bake for 20-25 minutes, until a toothpick or tester comes out with a few crumbs still on it.
Remove from oven and allow to cool in pan for 10 minutes before turning out.