Mix the yeast, water, and sugar together and let the mixture stand for 10 minutes. Add the flour, oil, and salt and knead into a dough. Let it sit for 1 hour.
Roll out the yeast dough on a work surface generously sprinkled with flour, spread the Nutella over it, then roll it up from both outside edges into the middle. Cut the double roll in half lengthwise so you end up with two individual rolls.
Position the rolls in a circle on a sheet pan lined with parchment paper. The ends of both rolls should be touching.
Use scissors to cut the wreath into segments a bit less than an inch thick, and pull them apart so they alternate between pointing inwards and outwards.
Generously coat the wreath with a whisked egg yolk and bake for 25 minutes in an oven preheated to 350°F.
Place a little bowl of Nutella in the middle for dipping, and decorate with fresh mint leaves, red currants, and blueberries. Dust everything with powdered sugar.
