Prepare a large bowl in which to make the sponge batter. Cream the butter and sugar in the bowl until fluffy before beating in the eggs one at a time. Once the eggs are well beaten, beat in the vanilla extract.

Mix together the flour, salt, and baking soda in a different bowl. Add a little of this mixture into the batter and beat well, then do the same with a little of the milk. Repeat this process until all the flour mixture and milk has been beaten into the batter.

Preheat an oven to 350 degrees. Take paper-lined muffin cups and fill them two thirds full. Bake the batter in the oven until a toothpick inserted in the center of the sponge comes out clean. This should take roughly 20 minutes.

When ready, take the cups from the oven and allow them to cool for 10 minutes before placing them on wire racks to cool completely. While they are cooling, make the frosting.

Beat vanilla extract and butter in a bowl until thoroughly blended. Gradually add the sugar and beat the mixture again until smooth. If the frosting is to be colored, mix in the desired food coloring. Frost the cupcakes and top them with any desired decorations.