Apple Coffee Cake

My roommates went apple picking and came back with such an abundance of apples that I have been able to make this cake three times in the last two weeks, and every time it is has been finished within two days! It's so quick and simple, but also so moist and delicious that you will want to find the best hiding spot for it so that you can gobble it down all by yourself. This recipe was one my mom always makes and is adapted from Anne Lindsay's Smart Cooking recipe for cinnamon coffee cake.
Ingredients:
1 cup plain yogurt
1 tsp baking soda
1/4 cup butter (softened to room temperature)
1 cup lightly packed brown sugar
1 egg
1 tsp vanilla
1 1/2 cups all purpose flower
2 tsp basking powder
3 Apples (I like Macintosh but you can use Cortland or any other red apple) peeled and sliced
topping:
1/2 lightly pack brown sugar
1 tbsp cinnamon
Directions:
Preheat oven to 350 degrees F and grease and flour a a square 9 inch baking pan. In a small bowl mix together the yogurt and baking soda and then set aside (the mixture will increase in volume because of the baking soda). In a large mixing bowl, mix together the butter and sugar until throughly mixed. Add in the vanilla and egg and beat well. In another bowl, sift together the flower and baking powder. Add the yogurt mixture and flour mixture to the butter/sugar mixture alternating between the two (add a little bit of each the beat, add a little more then beat etc).

In a small bowl combine the topping of brown sugar and cinnamon. Spread half of the cake batter into the bottom of the cake pan. Line up the apples along the top to create a single apple layer (don't have to overlap). Sprinkle the apples with half of the topping mixture.

Spread the remaining cake batter on top of the apple layer. Sprinkle the remains of the topping mixture on the top. Put in the oven for 45 minutes, or until a toothpick inserted comes out clean. Allow to cool on a dry rack for 10 to 15 minutes before eating.