In a medium-sized bowl, stir together yeast, water, and brown sugar and let stand for five minutes. It should get foamy, but don't worry too much if it doesn't. You aren't looking for giant foam, just a few bubbles.
Mix in flour, salt, buttermilk, and butter. Stir until the dough starts to come together.
Lightly flour a clean surface (so the dough won't stick to it) and dump the dough ball onto that surface. Knead it until the dough is smooth and elastic - about six minutes. The dough is really easy to work with - you shouldn't have too many problems with it sticking.
Coat the mixing bowl with oil, put your dough ball into it, cover, and set in a warm place to rise until doubled in size (about two hours).
Once the dough has risen, punch the dough down and split it in half.
Roll half of the dough into a 1/16" thick rectangle and cut into six even-ish strips. (You'll see from my photo below that I don't get caught up with perfection.)
Spread Nutella on top of the first strip. Then, top with banana pieces.
Top with second strip and repeat step 7.
Continue layering strips and banana slices until you reach the top strip. Do not coat the top of the last strip in Nutella or bananas.
Cut the layered dough into 6 sections of equal length.
Turn each section onto its side and place into a depression in a greased cupcake tin. It will not come to the top of the tin. Don't worry; there's still lots of rising to be done.
Repeat steps 6-11 with the second half of the dough.
Set the cupcake tin in a warm place and let the dough rise for another hour.
Preheat oven to 375 F.
Bake for 20 minutes or until the bread just begins to brown.