Preheat oven to 300°F. Butter or grease a bundt pan. Sift together flour, baking soda, salt, cinnamon, and nutmeg. Mash together ripe bananas and lemon juice. Set aside.
In an electric mixer, cream together butter, sugar, and brown sugar. Add eggs one at a time. Add vanilla. Add yogurt. Stir in dry ingredients until combined. Stir in banana and lemon juice mixture.
Evenly spread in a bundt pan. Bake for 65-70 minutes, until golden brown and a toothpick inserted, comes out clean. Immediately place in the freezer for 45 minutes. Remove pan from freezer; take the cake out and place on a cooling rack (or wherever you want it to be when you drizzle ganache).
Nutella Ganache
In a small saucepan heat heavy cream to just before a simmer. You want the cream to be warm enough to melt the Nutella, but not curdle.Place Nutella in a small bowl. Slowly pour heated cream into Nutella while whisking until combined; whisk in sea salt.Drizzle over cake. Recommended: place cake on a cooling rack that's on top of parchment paper for easy cleanup.
Notes
Every Banana Cake recipe I've seen has the "freezer trick" - it's said to keep the cake extra moist. I honestly just jumped on the bandwagon with this one, and had the extra time each time I made it, so if you choose not to freeze it after baking - let me know how it turns out!