Preheat the oven to 350 degrees F. Spray two 12 cup muffin tins with nonstick spray.
In a medium bowl, sift together the flour, baking powder, baking soda and salt.
In a separate bowl, use an electric mixer to combine the butter, sugar, Stevia and egg. Mix until well combined. Add the dry ingredients to the butter mixture alternately with the apple juice. Stir in the apple and walnuts.
Prepare the cheesecake layer: In a medium bowl, use an electric mixer to combine the cream cheese, sugar and Stevia. Then mix in the egg and vanilla.
Spoon a small amount of muffin batter into 18 muffin tins (about ½ of the tin). Spoon about a tablespoon of the cheesecake batter on top of each tin of muffin batter. You may be able to spoon a little more than that if you find that you have more batter to use. Top each cheesecake layer with another small spoonful of muffin batter. Top each with a few apple and walnut pieces.
Bake for about 18 to 20 minutes, or until the muffins are cooked through.