Banana Cake with Nutella Buttercream

ripe bananas, mashed

granulated sugar

light brown sugar, lightly packed

vegetable oil

large eggs, room temperature

sour cream (or buttermilk)

pure vanilla extract

all-purpose flour

baking soda

salt

toasted hazelnuts (measure before grinding) finely ground

Nutella Buttercream

unsalted butter, at room temperature

jar of Nutella

sifted confectioner's sugar

to 6 Tbsp heavy cream (or milk)