From: Art of Gluten-Free Baking (http://artofglutenfreebaking.com)
inspired by The Wooden Spoon Dessert Book, by Marilyn M. Moore
Yield: 1- 8 in x 8 in cake
For the cake
For the icing
Preheat oven to 350 degrees F/180 degrees C/Gas Mark 4
Grease and flour an 8 in by 8 in pan with extra butter and tapioca flour
In a small bowl, mix together flour, salt, baking powder, and baking soda
In a large bowl, beat together butter and sugar until creamy. I use a hand mixer to do this, but you can use a whisk. Add the egg and beat until fluffy—about 1 minute. Add the lemon zest and beat until combined.
Add the flour mix and buttermilk alternately in several batches, beginning and ending with the flour mix.
Scrape batter into prepared pan and smooth top.
Bake at 350 degrees F until tester comes out clean, about 30 minutes.
While cake is baking, make the icing. In a small bowl, whisk together all ingredients until creamy.
Cool in pan for 5 minutes. Then spread icing over entire surface of warm cake and allow to cool. Cake may be served warm or cold.
Store in an airtight container for up to 5 days at room temperature.