Preheat oven to 350. Spray a 9 x 9 baking dish with cooking spray.
In a bowl with an electric mixer cream the butter and sweetener until light and fluffy. Add the coffee, 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. Spread in the prepared baking dish.
Bake for 25-30 minutes until the cake it set. Cool completely.
Meanwhile, in a medium saucepan combine the 1 cup brewed coffee with the half and half and ¼ cup sweetener. Simmer until reduced by half, about 30 minutes. Cool completely.
When the cake is cool poke small holes in it. Pour the cooled coffee mixture on top. Let it soak in for at least 1 hour. At this point I put the cake in the fridge overnight. I prefer it thoroughly chilled.
To make the whipped cream topping whip the cream with an electric mixer until peaks begin to form. Sprinkle the instant coffee and sweetener on top. Add the vanilla. Continue mixing until well incorporated. Do not overbeat.