"Very simple but delicious dessert - not too sweet, but satisfies one's chocolate needs. Can be served immediately or cooled for at least 1 hour and reheated at 375 degrees F (190 degrees C) for 10 minutes. Serve with vanilla ice cream (such as Breyer's®)."
Preheat oven to 375 degrees F (190 degrees C). Grease 6 glass custard cups; place cups on a baking sheet.
Beat egg whites and sugar together in a bowl using an electric mixer until stiff peaks form, 4 to 5 minutes.
Heat chocolate chips and butter in a pot over low heat, stirring frequently, until melted, about 5 minutes. Remove from heat. Add in 1 egg yolk at time, stirring continuously. Add water and flour, stirring continuously. Fold in the beaten egg whites until just combined. Fill each custard cup about 2/3 full with batter.
Bake in the preheated oven until cakes rise slightly over the top of the cups and cracks form on their surface, 15 to 18 minutes.