Preheat your oven to 160°C. Grease or line a standard 12-cup muffin tin or 9-inch cake pan and set it aside. Transfer the dry ingredients to a large bowl and create a well in the centre. Add 8 tablespoons (112 g) of melted and cooled unsalted butter, 2 eggs (100 g, weighed out of shell) and 1 egg white (25 g) at room temperature, beaten, and 2/3 cup (5 1/3 fluid ounces) lukewarm water, and 2 teaspoons pure vanilla extract, mixing to combine well after each addition. Fill the wells of the cupcake pan 2/3 of the way full, or transfer the cake batter to the prepared 9-inch pan. Place in the centre of the preheated oven and bake until a toothpick inserted in the centre comes out mostly clean, or with a few moist crumbs attached (about 19 minutes for cupcakes; about 28 minutes for the cake). Remove from the oven and allow to sit in the pan for at least 10 minutes before transferring to a wire rack to cool completely. Makes one 9-inch cake or about 18 cupcakes.