1 ½teaspoonsvanilla extract(Clear vanilla extract helps keep the cake a brighter white, while pure vanilla extract adds a slight tint. Use whichever you prefer.)
Heat the oven to 350°F (177°C). Lightly butter a 10-ounce ramekin and set it aside.
In a medium bowl, whisk together the melted butter, sugar, egg white, and vanilla until smooth.
Stir in the self-rising flour, then add the cream and mix until fully combined.
Pour the batter into the prepared ramekin and place it on a rimmed baking sheet.
Bake for 20 minutes or until a toothpick inserted in the center comes out clean.
Let the cake cool on a wire rack.
Make the Frosting
While the cake cools, make the frosting. In a bowl, mix the sifted powdered sugar, butter, vanilla, and cream by hand or with an electric mixer until smooth.
Once the cake has cooled, frost it inside the ramekin or remove it first. To remove, run a thin knife along the edges, place a plate on top, and flip it over.
Spread the frosting over the top and sides, then add sprinkles if desired.
Notes
Read the recipe first. Review the full recipe and Ingredient Notes before starting. This cake comes together quickly, so it's best to have everything measured and ready.
Measure ingredients accurately. For flour, stir it in the container, then spoon it into a dry measuring cup and level it with a knife. Scooping directly from the container packs the flour too tightly, adding more than needed.
Don't overmix. Stir just until the ingredients are combined. Overmixing can make the cake dense and tough.
Use the right pan. A 10-ounce ramekin works best for this cake. To make a small white layer cake, double the recipe and use two ramekins.
Note: This recipe uses self-rising flour. To substitute with all-purpose flour, mix ½ cup all-purpose flour with ¾ teaspoon baking powder and a small pinch of salt (less than ⅛ teaspoon). Stir well and use in place of self-rising flour.