Preheat the oven to 350°F. Grease and flour a 9-inch round cake pan. In a large mixing bowl, cream together the butter and sugar until light and fluffy. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

In a separate bowl, whisk together the flour and baking powder. Gradually add the dry ingredients to the wet mixture, alternating with the milk, starting and ending with the flour.

Pour the batter into the prepared cake pan and bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.

In a mixing bowl, combine powdered sugar, egg whites, and lemon juice. Beat on high until stiff peaks form. Adjust the consistency with water or powdered sugar as needed.

Apply a base layer of royal icing using an offset spatula. Using a piping bag with a star tip, create rosettes, swags, and other decorative patterns. Layer the designs carefully to create a 3D effect.

Slice the cake into 8 pieces and serve with your choice of beverage. Consider pairing with a light tea or sparkling cider for a balanced experience.

Keep the cake in an airtight container at room temperature for up to 3 days. For longer storage, refrigerate for up to a week.