Preheat oven to 375 degrees F (190 degrees C). Line 30 cupcake pan cups with paper liners.
Sift the self-rising flour and salt together in a bowl.
In another bowl, beat the unsalted butter and sugar with an electric mixer until light and fluffy.
Beat in the eggs one at a time, beating each egg until incorporated before adding the next. Mix in the vanilla extract and lemon zest.
Gently beat the flour mixture into the butter mixture, one third at a time, alternating with half the milk and half the lemon juice after each of the first 2 additions of flour. Beat until just combined; do not over mix.
Fill the prepared cupcake liners with batter 3/4 full, and bake in the preheated oven until a toothpick inserted in the center comes out clean, about 17 minutes.
Let the cupcakes cool in the pans for about 10 minutes before removing them to finish cooling on a rack.
To make the icing
In a medium bowl, beat the butter, powdered sugar and lemon juice together until light and fluffy, about 1-2 minutes with an electric mixer. Mix in the vanilla and add 1-2 teaspoons of milk to adjust the consistency, if necessary. It should be creamy and spreadable. Stir in the 1 teaspoon lemon zest.
Drop a tablespoon or two of the frosting on each cupcake and spread until smooth. Top with a few wild violets if desired.