Preheat oven to 350 degrees. Spray a 12 cup non-stick or silicone bundt pan with cooking spray.
In a large mixing bowl cream together, butter, applesauce, brown sugar, white sugar and sugar substitute. Add in egg substitute and vanilla extract and mix well. It might look slightly separated but that is o.k.
In another bowl whisk 2 1/2 cups flour with baking powder and salt; set aside.
Add flour mixture to butter mixture in three additions, alternating with sour cream.
Re-use flour bowl to toss blueberries and zest with remaining teaspoon flour.
Spread batter in prepared pan.
Bake cake on bottom rack of oven until a toothpick inserted into center comes out clean, about 60 to 70 minutes.
Cool in pan 20 minutes then invert onto a wire rack.
Make a simple glaze with icing sugar and lemon juice or dust with icing sugar just before serving.