Prepare the Cupcakes:

1. Preheat the Oven: Set your oven to 350°F (175°C). Line a cupcake tin with 4 liners.
2. Mix Dry Ingredients: In a small bowl, whisk together flour, sugar, baking powder, and salt.
3. Cream Butter and Sugar: In another bowl, beat the softened butter and sugar until light and fluffy.
4. Add Wet Ingredients: Add the egg white, vanilla extract, and lemon juice (or vinegar), mixing well.
5. Combine Everything: Alternately add the flour mixture and milk, starting and ending with the flour. Mix until just combined.
6. Add Food Coloring: Stir in pink or red food coloring, if using, until the desired color is reached.
7. Fill Cupcake Liners: Divide the batter evenly between the 4 cupcake liners, filling each about ¾ full.

Bake the Cupcakes:

8. Bake: Place in the oven and bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean.
9. Cool: Let the cupcakes cool in the pan for 5 minutes, then transfer to a wire rack to cool completely before frosting.

Prepare the Frosting:

10. Beat the Butter: In a bowl, beat the softened butter until creamy and smooth.
11. Add Powdered Sugar: Gradually add powdered sugar, mixing well after each addition.
12. Add Vanilla and Milk: Stir in vanilla extract and milk (or heavy cream) to reach the desired consistency.
13. Add Food Coloring: If using, mix in pink or red food coloring.

Frost and Decorate:

14. Pipe or Spread the Frosting: Once cupcakes are fully cooled, frost them using a piping bag or a spatula.
15. Decorate: Add heart-shaped sprinkles, fresh berries, or edible glitter for a festive touch.