Preheat oven to 350 degrees F. Line cookie sheets with parchment paper or lightly grease.
In a large bowl, stir together the Rice Flour Blend, baking powder, guar gum and salt.
In the large bowl of an electric mixer, cream the ¾ cup buttery sticks and sugar together on low until combined. Beat on medium speed for 2 to 3 minutes, or until light and airy. Blend in the water and vanilla extract. Slowly add the flour mixture while mixing on low. Mix until fully incorporated and forms a dough.
Roll dough into 1 1/4" balls and place on prepared cookie sheets. Flatten slightly. Bake 10 to 12 minutes, or until crackled on top and not quite brown around edges. Cool on cookie sheet 5 minutes before transferring to cooling rack. Cool completely before frosting.
To make frosting, blend butter, confectioners' sugar and vanilla. Add water to reach desired consistency. Frost cookies and top with sprinkles.
Notes
*I used guar gum since it's what I had on hand, but I think xanthan gum would work too. If you are using a flour blend that already contains xanthan or guar gum, add an extra 1/2 teaspoon gum.** I found that the cookies made with real dairy butter had to bake a little longer (about 12 - 14 minutes). If using unsalted dairy butter, add an additional 1/4 teaspoon salt. Also, I found that dairy butter made the cookies spread out more while baking, but they are still soft.Additional Notes:
The dough does not have to be refrigerated before baking, but you can keep it in the fridge until ready to bake. Just let the dough get to room temperature.
I don't know how well these would work as cut-out cookies since they do spread out while baking.
Don't over-bake or flatten the dough out too much, otherwise the cookies will turn out crunchy.
The cookies will be much sturdier once they have completely cooled.