Make the cupcakes. In a large mixing bowl, blend well the sugar and softened butter. Blend in the eggs, one by one.
Make the sour milk. To 1 tablespoon lemon juice, add enough milk to bring it to 1 cup. Let it sit for 5 minutes. It will curdle.
In another bowl, mix together the dry ingredients (sweet rice flour, baking soda, baking powder, and salt).
To the butter/sugar/egg mixture, alternately blend in the dry mixture and sour milk. Blend well. Rice flour lacks gluten, so the mixture will become fluffy as you blend.
Fill cupcake holders about 3/4 of the way. Bake at 350 degrees F for 17 - 20 minutes. When cupcakes are slightly golden brown and a toothpick comes out clean, the are perfect.
Make the cream cheese icing. Blend well the cream cheese and butter.
Blend in the powdered sugar, a little at a time.
Blend in the lemon juice, a tablespoon at a time, tasting as you go.
Keep the icing chilled in the refrigerator until ready for use.
Spread on top of cupcakes after they've cooled off.