Preheat oven to 375 degrees F. Spray muffin tins with cooking spray or line with cupcake liners, and set aside.
Add butter and sugar to mixing bowl and beat on medium-high speed until smooth.
Add eggs, 1 at a time, mixing until combined with each, then mix in vanilla extract and orange zest.
In a separate bowl, combine flour, salt, and baking powder. With the mixer on low speed, add the flour mixture to the wet mixture. Mix until just combined.
Mix in the applesauce, and then stir in the blueberries.
Divide among muffin tins, filling only about 2/3rds full. Bake for 25-30 minutes, or until toothpick inserted in the middle comes out clean. (If making mini muffins, bake for 15-18 minutes.) Remove and allow to cool, then enjoy!
Notes
*You can use all-purpose flour if you don't have cake flour (so 2 cups of AP flour, instead of 1 cup of each AP and cake flours.)