Preheat oven to 325?F and spray 6 1/2-cup capacity custard cups with nonstick cooking spray. In a medium saucepan, combine milk, Baileys, chocolate chips, sugar, flour and butter. Cook, stirring constantly with a whisk, over medium high heat until mixture begins to boil. Boil for 1 minute and remove from heat. Let cool slightly and stir in egg yolks. In a small mixing bowl, beat egg whites and salt until soft peaks form. Stir 1/3 of beaten egg whites into chocolate mixture until well combined. Gently fold in remaining egg whites with a rubber spatula until thoroughly incorporated. Place custard cups in a 9-by-13-inch pan and fill pan to a depth of 1 inch with hot water. Bake for 20 minutes. Dust with powdered sugar if desired and serve immediately.