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, beat the cream in a chilled bowl with an electric mixer set on Low until the cream begins to thicken. Add the confectioners' sugar and lemon juice, a little at a time, beating after each addition, until fully incorporated. Increase the mixer speed to High, and beat until the icing forms soft peaks, about 5 minutes. Spread on the cooled cupcakes. Refrigerate leftovers.