Whisk together warm water, yeast, and a pinch of sugar in a bowl and let rest until fluffy for 5-7 minutes
In a large bowl, combine flour, milk, remaining sugar, salt, eggs, vanilla, and yeast mixture
Mix until combined for about 3-4 minutes, then cover with a clean kitchen cloth or plastic wrap and let rest at room temperature for 10-12 minutes
Knead the dough by stand mixer or hand for 12-15 minutes, adding room temperature butter gradually
Cover with plastic wrap and refrigerate overnight or keep at room temperature for 1-2 hours until doubled in size
Punch down the dough and place on a floured counter, then roll to ½ inch thick with a rolling pin
Cut dough using a circle cookie cutter, ensuring each piece weighs 65-70g
Place pieces on a parchment-lined baking tray, cover with a clean kitchen towel, and let rest at room temperature for 30-45 minutes (40-45 minutes if refrigerated overnight, 25-30 minutes if at room temperature)
Heat oil to 350°F and fry donuts on both sides until golden brown
Remove donuts from oil and dip into the sugar and cinnamon mixture
Using a pastry bag, fill donuts with hazelnut chocolate cream
