Preheat oven to 350 and spray cake pan.
Combine butter and yogurt in mixing bowl and whisk well. Add sugar and vanilla and beat with mixer on medium speed for 3 minutes. Add egg replacer and continue to mix.
Combine flour, xanthan, baking soda, and salt in separate bowl.
Add dry ingredients to mixing bowl, alternating with the rice milk/lemon juice mixture. Begin and end with flour mixture. Mix well.
Pour batter into pan and tap once on counter to remove air bubbles.
Bake at 350 for 30 minutes. Let cool and then frost.