In a medium-sized 3 quart bowl, beat sugar and butter until creamy with a hand mixer on moderate high speed for about 3 minutes.
Add 1 egg and beat with the batter from Step 1 on a low speed. Add the other and continue beating.
Add mashed bananas and vanilla to the batter and continue beating on a moderately low speed.
In a separate medium sized bowl, mix your dry ingredients together with a fork or whisk: flour (unsifted is fine), cream of tartar and salt.
Gently stir in dry ingredients using a rubber spatula from Step 4 to your batter in Step 3 for a maximum of 2 minutes. Add blueberries and dried cranberries and continue folding/stirring for 30 seconds or less. (Optional: in lieu of dried cranberries, use white chocolate chips.)
Bake at a 350°F oven (176.667°C) for 45 minutes or until a skewer comes off clean.