In a bowl with an electric mixer cream the butter and sweetener until light and fluffy. Add the yogurt and vanilla and beat until combined. Add the eggs one at a time mixing after each. Stir in the flours, baking powder, and salt until thoroughly combined. Divide batter between 4 round cake pans lined with parchment paper and cooking spray.
Bake at 350 for 20-22 minutes until the cake springs back when lightly pressed with your finger and the edges are golden. Cool completely.
Icing Instructions: Beat the butter and sweetener until smooth. Add the cocoa powder and half and half. Beat until smooth. Add the yogurt. Use to ice the cooled cake.