In a mixing bowl, combine yeast and warm water, stirring gently to combine. Let sit for 10 minutes, until foamy.
Combine flour, sugar, salt, egg yolk, oil, chocolate chips, sprinkles, and yeast mixture in a bowl and stir until just combined. Dough will be shaggy.
Turn dough out onto a floured surface and knead for 5-7 min by hand (or by using bread hook attachment on your mixer). Dough should be smooth and elastic. If it's too wet, add a little bit of flour.
Coat a separate bowl in oil, put the dough ball in , and turn to coat the entire ball in oil. Loosely cover with plastic wrap and allow to rise in a warm place for an hour (an oven with the light off works great).
Let rise 1 hour, then punch the dough down to deflate it, and allow to rise another hour.
Preheat oven to 350F.
After the second rise, cut into 4 pieces. Roll each piece out to a roughly 1 foot long 'snake', fold, twist, and tuck ends under to create a 'braided bun' shape on a lined baking sheet.
Brush buns with egg was and top with additional sprinkles. Let rest while oven preheats.
Bake at 350 for 22-26 min, until buns are lightly golden.
Remove buns from oven and allow to cool for an hour. This will allow them to soften up. Serve with a side of Nutella for dipping, or enjoy them on their own!