Preheat oven to 350°F. Spray a nonstick Bundt pan with cooking spray.
Sift cake flour, baking powder, and baking soda together into a mixing bowl.
In a large mixing bowl using an electric mixer, cream the butter until light and fluffy. Add Splenda Stevia Sweetener and egg; mix until smooth. Add the egg substitute and vanilla extract; beat briefly to incorporate.
Add applesauce and half of the sour cream; mix until smooth.
Add the dry ingredients and beat on medium speed just until smooth. Add remaining sour cream and blend just until incorporated and batter is uniform.
Transfer about ¼ of the cake batter to a bowl; stir in brown sugar and cinnamon.
Place ½ of the remaining cake batter into prepared pan. Top with cinnamon batter and swirl with the tip of a knife. Top with remaining cake batter.
Bake for 50–60 minutes or until a wooden pick inserted near the center comes out clean.