Steps
1. Preheat your oven to 350°F (175°C). Lightly grease a small ramekin or oven-safe mug.
2. In a small bowl, whisk together flour, sugar, baking powder, and salt.
3. Add milk, vegetable oil, vanilla extract, and beaten egg. Mix until smooth and combined.
4. Pour batter into the prepared ramekin.
5. Bake for 18-22 minutes or until a toothpick inserted in the center comes out clean.
6. While the cake cools, prepare the buttercream by beating softened butter until creamy.
7. Gradually add powdered sugar, then vanilla extract and milk, beating until smooth and fluffy.
8. Once the cake is cool, spread the vanilla buttercream evenly on top.
9. Serve immediately and enjoy your single-serve vanilla cake!