Preheat oven to 350°F. Rub butter around the inside of an 8-inch (or two 6-inch) round cake pan(s) and line the bottom with parchment paper.
Whisk the Classic Gluten-Free Flour Blend, egg replacer, baking soda, baking powder, xanthan and guar gums and salt together in a large bowl.
In a stand mixer fitted with the paddle attachment (or with a hand-held mixer), cream the butter until white, about 2 minutes. Add the sugar and continue to beat until fluffy.
Add the eggs, one at a time, mixing after each addition until smooth.
Stir in the dry ingredients. Then stir in the vanilla and milk until smooth.
Spoon the cake batter into the prepared pan and smooth the top. Tap the pan on the counter top to eliminate any air pockets.
Bake on the middle rack for 16 - 20 minutes for two 6-inch pans (17 - 20 minutes for one 8-inch pan) or until a cake tester comes out hot to the touch. Do not open the oven during baking.
Cool the cake in the pan for 5 minutes before inverting onto a cooling rack. Cool completely before frosting or wrap with multiple layers of plastic wrap and freeze.
The Frayed Apron Classic Gluten-Free Flour Blend:
6 cups white rice flour
1 cup tapioca flour, also known as tapioca starch
Spoon flour into the measuring cup, use a butter knife to scrape across for a level measurement. Whisk to combine. Then measure as recipe calls for Classic Gluten Free Flour Blend. The Frayed Apron Egg Replacer (Leavening Agent):
1 Tablespoon tapioca flour or cornstarch
1 Tablespoon potato starch or arrowroot
1/4 tsp baking powder
Mix ingredients, then measure according to recipe for Egg Replacer. Xanthan Gum & Guar Gum Blend
1 Tablespoon xanthan gum
1 Tablespoon guar gum
Whisk together to blend. Measure and use in recipe.**Leftover flour can be stored in the freezer in a zip-locked bag.For Cupcakes:Fill 12 cupcake liners 1/2 way and bake for 16 minutes, until toothpick comes out clean and the cake is springy when touched.