Preheat the oven to 350°F. Grease two 8inch circular pans.
Mash Bananas. Set aside.
Whisk together flour, baking powder, baking soda, cream of tartar, and salt. Set aside.
Beat butter on high speed until smooth and creamy (about 2 minutes). Add both sugars and mix on high for another 2 minutes or until creamed together.
Add eggs and vanilla extract to the butter mixture. Mix until combined.
Add in mashed bananas. Beat until combined.
Add dry ingredients and milk, alternating between each until just combined.
Pour batter into the prepared pans. Bake for 40-45 minutes.
Turn out cake onto a wire rack for cooling.