One thing missing

I gathered all my supplies, finally ridding my counter of the rotting bananas. 

Cooking with Fannie Farmer makes me feel wholesome and connected to my grandmothers.

I could just taste the warm, hearty banana bread!

And I remember thinking, "This is a really simple recipe. Just a few basic ingredients." 

Thankfully, shortly before adding the walnuts and pouring the batter into the loaf pan, the light bulb turned on.  

Do you see what ingredient is missing?